in DUST AED ITS CONTROL bv U 0' '1. thth'H-.§l;l MICE GAY: STATE COLLEGE June 13, 1986. ._ THESu} l: 4~6I ‘_a~.o—‘ ~\"-/ / Dust has always been a nuisance because it is either infectious, irritating, poisonious, obstructive, abrasive, unsightly, or dangerous. .According to Dr. Bundencen, formerly health c0mmissioner of Chicago, sixty per cent more_pe0ple are dying of diseases caused by contaminated air than of all other diseases”, Dr. W. G. Humphreys of the United States Weather Bureau states that we inhale a million micro-sticks- and stones and a host of other things that are no part of a pure atmOSphere each time we breathopfl Such diseases as common colds, influenza, tuber- culosis, scarlet fever, diphtheria, whooping cough, and scores of others, are usually transmitted from person to person by air borne germs from out of the air, and not through.personal contact, A, cough - a sneeze, or even ordinary conversation from a person suffering from these diseases throughs literally millions of germs into the atmosphere. These germs are heavier than air, and in a perfectly clean atmOSphere would soon settle to the floor or the ground and do little or no damage. Unfortunately, however, the air is not clean, and germs which find their way into the atmos- phere, lodge on dust particles where they float for hours awaiting an Oppor- tunity to attack an unsuspecting victim. It is said that the weight of food eaten daily by the average person is three and one half pounds and the weight of the air breathed is thirty- five pounds. It is further stated that forty per cent of our energy is derived from food and sixty per cent from the air we breathe. Thesefacts surely present vividly the importance of prOperly cleaning the air in which We live. .A ir borne dust, called pollen, of certain plants such as rag weed and golden rod are the cause of hay fever, and metallic dust such as lead” arsenic, and.mercury cause poisoning. These dusts affect humans in.three ways, depending upon the manner or method of contact, or ingress into the body. First by contact with the skin, or exposed mucous sur- faces producing the so-called dermatoconioses. The dermatilis of the skin on the necks of the workmen who carry cement, or similar substances that give off an irritating dust; irritation of the eyes and eyelids 9f workers in the bore: mills; and some of the trade exzemas are typical examples of these conditions. These skin lesions are well known to the specialist.. The second class of cases are caused by ingestion of dust thru.the nose and mouth. These are called enteroconcoses. Eliver states "The enteroconiosis of gastro-intestinal lesions induced by dust are less well defined bacteriological entities that the infections of the skin or lungs and yet they play an important part in poisOning by such metallic dust as lead, arsenic and mercury." Apart from such symptoms as vamiting, diarrhoea and colic, which these cause, there are well marked physical signs of poisoning present as, for example, the ”blue line“ on the gums in lead poisoning and the loose teeth and ulcerated gums in mercurial poisoning. The third class of disease caused by air dust is the so-called pneumonoconiosis, due to the inhalation of the particles. This class has received considerable study in the past, particularly from Pathological and symptomatic standpoint. Chalicosis due to stone dust; siderosis, due to metallic dust; anthracosis, due to coal dust; byssinosis, dun to the inhalation of cotton fibres, et cetera, are well recognized and thoroughly treated in the literature. Employees shOuld.be carefully instructed in the process and materials being handled if such precesses or material are toxic in their action on the body. Foreign language signs, talks, explanations, proper lhcker - clothing - bathing and washing facilities, the use - function and necessity for respirators and finally the tragic results of carelessness and.indifference to occupational disease hazards should be periodically and continuously instilled. This instruction must be continuous to be moet effective. The amount of blood and the percentage of hemOglobin are increased by sunlight and decreased by darkness. Smoke or dust intercepts the sun rays of the shorter wave lengths. These shorter waves, in addition to their effect in restricting bacterial growth, stimulate the powers of resistance to bacterial infection by their action on certain fatty sub- stances in the skin. Rickets, and other disturbances of the metabolism of lime salts, very important to health, result when the short or ultra- violet rays of the sun are excluded from the body. When the nutrition of the body is thus vitiated, it becomes more susceptible to bacterial infection. Soot has a definite bacterial action, probably due to the action of its contained germicidal acid and.phenols; it does not form a favorable nidus for the collection and distribution of bacteria. 0n the Other hand, soot, as it occurs in smoke, clouds, ngs, and as a non- transparent covering for streets and buildings, protects micro-organisms from.the destructive action of the sunlight. Bust from.grain and coal is as explosive as gunpoider under certain conditions, and has been known to wreck factories and elevators with terrific blasts. Small particles of dust get into the cylinders of on! auto- mobile motors and defeat the purpose of lubrication.by breaking the oil film which is intended to prevent metal to metal contact, and act: in much the same manner as a grinding compound. The result is excessive and unnecessary wear on pistons, cylinders, and bearings, stuhk pistons, and contaminated lubricating oil. Perhaps the most noticable thing abOut dust is that it gets into out homes and soils our walls, furniture, and clothing. You might ask:”Where does all this dust come from?" It comes from.everyWhere. There is lint from cloth, grains of soil, burnt out bits of stars, shreds of plants and animals that may have been dead thousands of years, tiny crystals of minerals, grains of pollen, spores of molds and yeasts, and dormant bodies of bacteria - so small that they can be seen only with the aid of the finest lenzes. Activities suCh as grinding, polishing, dyeing, handling, gilding, painting, mixing, cleaning, and pulverizing produce an enormous amount of dust. So you can see atmospheric dust is c0mposed of most everything. In thickly settled or industrial localities it c0nsists of about eightybfive to ninetybfive per cent of soot or carbon, the balance being a mixture of miscellaneOus substances including metallic, mineral, vegetable, and animal matter. Dust particles vary greatly in size as you can plainly see'by referring to figure 1. iLDust from industrial districts is be- coming more and more menacing, not only to health but to looks or beauty and life of Structures. SIZE AND CHARACTER|ST|CS OF AlR-BORNE COMPILED 8‘! W. SOLIDS G. FRANK RATE or Nggm‘ sags“: DIAM. mun 0 A A IN or SCALE OF IN sen. aria: 1": 33°33: titlwngtAiIEOTJ 9336 PAR- FOR c N TICLES AT MOS PH E R‘ C SPHERES AIR CONTAINING PARTICLE 5 '2 E IN IMPURITIES 0' .0005 03mm or mean mmi mpum-ngs "a (LINES 0s DEMARCATION Awaken.) A1 10' F. cun.(0eNsm-I) sooo _ L: PARTICLE: FALL WH’H 6000 —'—— "so _ INCREAsINe szocn'v ‘°°° _ 1:. ,,. a c-Vclocity eta/sec. 2°00 2 . a 2+— , a /___"2"'sTfiT z ._ T— _ :2 I; 3 Ks. c-Vdocity ftJmin. I000 g 2' o g 790 .015 .000365 — I; 800 *— — 3"; — ~—--1n .v : d-Dicm. 0f par-g 50° 3 ‘ If; _, 555 .6 00013 5 C=Z4.9VDs, ticI: In cm. _ __ _ -- A o 400 ‘ 5 ‘4 §_§ d D-Diom. of per— 200 :1 E _ I "_ is e > tick in Micron: 5 3 '28 " ‘ STOKES II 0‘ I ‘3‘ r '2' P LAW r-Rcdius of par- I00 9 ° “ m 53.1 15 .003“: z . . so ;. _ 7&3 .f , il‘INASQ. : has m cm. 60 —— g 2% E3 ‘3 we ego .0013 g 9, 98‘ cut/“c3. 40 E at» a £13 8 c.§"9 5.1;“. occdcration WI 20 e L3 32 ‘ E g: 1: s.-Du\slt_y of i2 8 :5 3 z a g t particle .0 I" g I .592 15000 .0365: 3 . 8 in is 6mm :1 F0II AIR A1 10 r. sz-Dcnsity of Air 6 r; 9, ‘u .5 .I40 600,000 .013 .._I c -300,4603o‘ (Very Smcu 4 ,- " 3T 2* a : mum to s.) I! a. '5' l; L - u C -.005925,D n J a 34E ‘ o “I n y-Viscosity of 2 9- :: u U U I— - - Z n. o g g :3 mr In pmses ' “I g a: I- a I: “' fl‘hs' 7st0‘ .365 H 3 “5‘4“0-7‘0" -B i. 5 gm; a” "5" "t {“5“- 0’ CUNNINGHAM‘S air at 70‘ F. -5 E" ‘ 9’ Ii ‘ ‘ 0024.4" soon" 1: ,1: HUGE A I0'5cm WI 55 3 ; PKR HR. 3 - . -4 :- n 73 Z 3 , & c-c'(I+K—?-) (Mean free 5 .‘LJ 2 m g? f ‘. path of go: I I ~ I ‘ E 5 2 La ‘ :2 m-lemo’ 3.551 '8 1'0 6‘ ' 3 fig "R “K WIN-5% PARTICLES move LIKE :1 m i E Kiri 0 6mm". 1.: GA: MOLECULES L M d 3" 1 F - g 3:: 3* ~ mm u, g €315.21; g: g I novenem 1 "' ("z 1' f " J I O I 02 2:; ' O R Gas constant 0, 1: 2 31ng “I: '4‘: g 0 15 no“ 35.9 s - B.$|6 x lo1 ' _g___ 1 “IT. 5 regal ; a? a u ‘ T - Absqute ( “W: n] p- ‘A N 3171’? 4 a w aha. N‘Nombcrof 603 u L o g In! its :3. ET OCCU m z u 365' one Ind-6.06: ,9_0I ' I 0 75am 2.53 COPYRIGHTED BY AMER‘CAN A|R FILTER O0..IN¢~ 57. I The products of combustiona of fuels that are injurious to stone may be divided, rOughly, into two clases:(l) Those that soil and render the buildings unsightly, that is, carbon, tar, ash, and their variOus com- binations; and (2) those that corrode and in general aid in the destruc- tion and weathering, that is, sulphuric acid, sulphurous acid, hydrogen suphide, hydrochloric acid, ammonia, the organic acids, etc. The latter group do apply to this discussion. The cation of carbon and ash, when not associated.with tar, is not extremely objectionable, as the simple process of brushing will remove either. Ihen, however, they'are sssociated.with tar, especially in the case of soot, they produce the most Objectionable kind of dirt. The tar causes the soot to adhere fhrmly to the surface with whidh it comes in contact, literally covering the object with a coating of black paint and.penetrating into the porous structure. ‘this coat is not readilly removed,'because it has adhesive preperties and.also because it is insoluable in water. Drastic measures such.as the use of solvents, scouring, or both, frequently are necessary. Steam cleaning has been used recently for this purpose. Soot that does not contain injurious constituents may, in fact, act as a protective coating. However, this coating is not uniform and.where metallic sur- faces are intended to be of decorative value, the effect is spoiled, if not entirely destroyed, by the mottled soiling. The remedy in such case is simple - Wipe off the dust. When the surface is covered'by soot con- taining tar, or soot and tar separately, oftentimes scouring is necessary to clean the surfiace, but this results in injury to the metal through abrasion. If the soot is allowed to remain, any intended decorative effect it destroyed in this case also. Particles of carbon deposited upon the paint apparently tend to increase the life of the coating, since the ultra violet light which affects the films is absorbed.at the surface. Paint darkened.when applied to test fences,erected in different localities in the United States; the tarry matter from dep03ition of soot seemd.to be throughly incorporatd in the film, Paint applied over a soot coated surface was attacked by the soot beneath as well as by that deposited on the exposed surface. Frequent washing of paint coatings is necessary, and paint must be renewed in less time in a smoky atmosphere than in one com- paratively free from smoke. Fine soot, as an impalpable powder, will go anywhere and everywhere that air does, and the tarry matter with it causes much of it to adhere firmly to any surface with which it comes in contact. Changes in atmospheric pressure produce changes in the air currents in shut—in or confined places, carrying the soot to the most unexpected corners. IA- common and striking example of this is the framed.picture, with little dark sprays of soot along the white mats or on the picture itself, where the air currents have reached the space behind the glass. 'gggause of the fineness of smoke particles, common air filters will not remove them, but a relatively new type of filter — ‘working on the ionization principle - has been deve10ped.whiCh will remove them. This filter will be discussed later. "The most notice- able damage of the dust of industrial districts is in impairing appear- ances and causing an enormous amount of extra, expensive, and.unnecessary Work and care in keeping working and living quarters in such condition as is required by peOple accustomed to the common standard of living. For the architect or decorator the market does not offer a paint or wall covering that is not susceptible to damage and the life of Which is not shortened'by dust. And the possibilities of the choice of colors for interior painting are limited.appreciab1y. Wall paper must be cleaned.more often in a dusty, sm0ky city and its life is much shorter than in a clean atmosphere. Lace curtains and hangings are soiled easily by dust and.must he washed.frequently. Dust is readily ground in a floor rug marring its looks and causing excessive wear. A ltogether, the cost of up—keep of paints, decorations, and furnishings isgfrcmltwo_to five times as mush as in a clean city. The Wind is constantly lifting dust into the air and carrying it about, and violent wind storms may spread dust over thousands of miles. In the autum.of 1933 a mud storm visited the eastern states. It was Just dust picked'up by the wind in.the western and middle western states that got mixed.up with a rain storm. In Buffalo, New York, the micro- sc0pe was turn upon some of this and it was possible to identify not only the material in the dust, but learn from whence it came. Sixteen different minerals, in tiny crystals, were present. There were threads of simple plants we call Algae, which live in stagnant waters; spores of low forms of other plants like the mosses, and the glassy shells of the more-plant- than—animal forms of life we call diatOms. This dust had originally come from some peculiar driedrup lake'beds that exist only in the mountains of British Columbia, and.had contained no water for perhapd.thousands of years . '- All over the earth the wind is at work tranSporting dust from one place to another. It is reaponsible for the miraculous “bloody" rains '(‘v H's heart‘s and snow storms that at times strike terrorAPf the simple peasant folk of southern.Eur0pe. These peOple, not having access to microsc0pe, have believed for ages that these storms are portents of evil days to come; that they are signs for telling pestilence, famine, or war. Yet the red color of the rains or snows is due only to fine dust that comes hundreds of miles across the hediterranean Sea, from the Sahara Desert in north A frica. Reddish soils are not found in southers Europe so it is easy to understand.the superstitious fear with which ignorant peOple have regarded these red rains and snows. Cyclones 0n the deserts carry aloft the fine red desert powder and scatter it over nearly all of western EurOpe. One violent storm in 1901 carried dust twenty-five hundred miles, and.a German meteorologist estimated that more than two Hullion tone were distributed over EurOpe, another like amount dumped into the Mediterranean, and one hundred fifty million tons sifted over northern Africa. When volcanoes blow their heads off, clouds of dust weighing thousands 0f tons are blown into the upper atmosphere, as high as fifty miles above the earths surface. Up in those regions there are no wind currents, and the dust must fall of its own.weight, a fall that may require many years. The greatest recorded dust storm in modern times was brought about by the eruption of Krakotoa, in the Malay peninsula in 1883. Dust rained down inches thick over a radius of a thousand.miles, and the sky over the greater portion of the earth was red for three days. DMst from Krakotoa is believed to have fallen over practically every portion of the earths surface. So you can see that it is impossible to prevent the production or distribution of dust. In fact it would be unwise to do SO. It is dust that gives blueness to the skies, and creates the gorgeous colors of the sunrise and sunset. Parado.:ically, dust is a health protector, tOO, for it scatters a goodly portion of the harmful rays of the sun which WOuld otherwise blind us. And, if it Weren't for dust, no rain nor snow could fall, and the earth would soon be parched to the dryness of dust. For, each drOp of water, each flake of snow, must have a particle of dust about which to gather itself else it Cannot form except under conditions of uper-saturation of moisture, conditiOns which rarely occur in nature. According to authorities the air in industrial districts contains from one to four grains of dust per thousand cubic feet. In order to Visualize what a small amount of dust this is, picture a room ten feet by ten feet by ten feet; there you have one thousand cubic feet. ITOW divide one pou;;d dust into seven thousand equal parts Imifovmly in the air of this room, and you have one grain of dust per thousand cubic feet. This air would appear quite clean. In fact you could easily distribute twenty grains of dust in the same amount of air and it would not be visible eJccept in a strong beam of light. This redatively small amount of dust may seem insignificant until you figure it out for some particular engine 01‘ empressor; for instance the displacement of a. five .undred horse power Diesel is approximately cubic feet per minute. Operating ten hours per day this engine would draw in eight million four hundred thousand cubic feet of air per week which will contain 1.2 pounds ( at 1 grain /lo'3o cu. ft.) to 4.8 pounds ( at 4 grains/1070 cu. ft.) which would cause considerable wear on the cylinder blocks, etc. The human system is normally equipped to guard against inhaled dust and.germs in natural quantities only. It is certainly not prepared to combat the abnormal COnditions found in modern congested cities. When the normal dust and germ content is exceeded, the respiratory membrane is overtaxed, internal resistance to disease is overpowered and the chances of mass infection are exceedingly great. It is net yet commercially possible to completely cleanse and sterilize the atmosphere; indeed it is very doubtful if completely cleansed, sterile air is of any more benefit to the human system than is distilled water. But the respiratory system should not be subjected to a greater d0se than that for which it was designed. Dust and germs have been treated as one for the reason that it is almost impossible for germs to exist and be transposted in the atmosphere Without the use of dust as a medium of travel. Remove the dust and the germs go with it. EErJODS OF 0* EAIIIG AT. CSPhCP IC AIR. The efficiency of an air cleaner may be expressed as the ratio between the quantity of dust extracted by the cleaner from a given volume of air and.the quantity of dust contained in the same air tolume before cleaning. This efficiency for any given air cleaner varies widely, depending on the quantity and the character of the dust in the uncleaned air and also on the dirtiness of the cleaner and the velocity of the air passing through it. Therefore you can easily see that these qualifying conditions must be stated.when the efficiency is given if the efficiency is to mean anything. The only thing that really mat ers in regard to efficiency is to establish the maximum quantity of dust which -F Itevcd GU" my be perlmitted in the filterAwithout being harmful in the partifular case under consideration and to insist that the air cleaner perform accordingly. The requirements for cleaning efficiency are, therefore, elastic, depending upon the exact purpose of installation. Expressed in general terms, the efficiency should be so high that tr e dust left in the filtered air can cause no harm or be a nuisance in the particular work for which the air cleaning equipment id provided. Take as an exagple the drying; room of a film laboratory. In this case even a very minute quantity of dust will cause trouble, and it should be required that the filtered.air at no time shall contain more than .01 grains of dust per thousand cubic feet. In an automatic telephone exchange the requirements hhould.be equally high. For turbo-genexator cooling, the quantity and the character of the dust in the filtered air should be such that it cannot be caught in the generator windings, but will pass through inauspension in the cooling air . A hi gher degree of cleaning than this is nOt needed.and therefore is nOt worth paying for. If the filtered air at no time contains more than .10 grains of dnst per thouéand cubic feet, this requirement is fully met. For general building ventilation the filtered air must he so clean that no dust can be seen or felt, nor should it settle in the rooms to be ventilated. A'higher degree of cleaning than this is unnecessary and would.mean a waste of money. These requirements are filled if the air at no time contains more than .10 grains of dust per thousand cubic feet. FILTER RESISTAECE Filter resistance is understood as the difference in static pressure in front and behind the air cleaner and it is a factor in the amount of power required to clean the air. As a general preposition it is true that the cleaning efficiency of any apparatus is more or less pr0portional to its resistance or its power consumption. The amount of work performed is always prOportional to the power expended, therefore, claims of an extremely low resistance should be listened to with suSpicion. Every individual filtering apparatus has a definite resistance at its rated fair flow and.at a given degree of dirtiness of the filter. Sufficient fan power must be provided to overcome this resistance. The resistance of an air filter in a clean state is only of theoretical interest. The thing that really mattrs is the Operating resistance under average con- ditions of dust accumulation in the filter. It is on this factor that the engineer or architect should center his attention in selecting an air filter. 'With increasing dirtiness of the filter the resistance increases and at the same time the air volume is gradually reduced. It becomes one of the prime requirements Of an air filter, therefore, that its Operating resistance must never go so high as to materially cut down the volume of air going through the filter. In a generator installation this reduction in volume will result in overheating and sometimes in the burning out of the generator, In building vemtilation it will result in an insufficient volume of fresh air being supplied. CLEARING OF THE FILTER host air cleaners used for atmospheric air are not self cleaning therefore they must be taken out periOdically to have the accumulated dust removed from them, or else replace the filter with a new one. Cheese cloth filters are cleaned by brushing, snaking, heating, or With the help of vacuum cleaners. Even air washers must be shut down periodically for removing the dirt sediment; for cleaning the spray nOzzles,etc. Metal filters with viscous-coated filter medium are jperiodically cleaned by washing in warm water and soda or by being 'blown or washed Out with a steam or water hose. It is an essential requirement of any filter that it can be thoroughly cleaned.with as little expenditure of time and labor as possible. If all the accumulated dust cannot be removed in the washing process the filter will not go back to its original resistance, and the result will be that a fraction of an inch water guage will be added to the resistance with each washing opera- tion. .A s filters of this type must be washed every two to ten.weeks, it is apparent that cumulateive effect of this added resistance will be ‘Very serious. CHARACTER OF THE FILTER hEDIUE The material in a filter which catches and.binds the dust is here referred to as a filter medium. The filter medium should be of such a character that it stays in the filter indefinitely and that no part of it can be torn loose and carried into the clean air duct. Filtering materials which have a tendency to rust, disintegrate, or break:up into small particles are, therefore, objectionable. If such a filter were employed to clean the air used.in drying food products, or for cooling turbo-generators, for instance, the consequences might be very disastrous. TESTS OH.AIR FILTERS Tests on air filters, to be of any practical value, should Heter- mine; (1) he cleaning efficiency (2) the Operating resistance'under conditions which correspond to permanent service conditions, and (3) to what extent the accumulated dust can be removed from the filter and the amount of time and labor involved in the cleaning Operation. The average dust concentration in atmOSpheric air being comparatively low, it is evident that it takes a long time for a test filter to accumul ate enough dust to enable the observer to draw correct conclusions as to its behavior under permanent Operating conditions, in an actual installation. It may take six to ten weeks of continuous Operation of the filter, depend- ing on the dust concentration in the air. Such tests can be greatly accelerated.by artificially introducing a higher dust concentration into the air. At any rate no conclusions as to points t“o and three above can be drawn from such tests, unless the filters are charged.with the Inaximum quantity of dust which they will normally accumulate in an actual installation. For viscous-coated metal filters this corresponds to about one half to one pound 0f averge dust per fi ter unit of twenty inch by twenty inch front area. The washing test should be repeated several times ir order to give average and fair indication as to the increase in resistance for each washing. In making tests to determine the comparative merits of campeting equipment, it is advisable to invite representatives of all the sompeting makes to be tested, as manufacturers generally know more about their own éhuipment than any one else, and they often make valuable suggestions as to the tests. H0"! DUST IS 65.27333 A ir cleanérs are based on one or more of the following principles: (except the electrical filter) (1) screening action: everyone known how a gravel screen works; the pieces which are smaller than the meshes go through and those which are larger are kept back. The pieces which are just a trifle larger than the free Openings are caight in the meshes. .A screen used as an air filter works in exactly the same manner. float of the dust particles in the air are too small to be seen by the naked eye and.even the finest screen is, therefore, an inefficient air filter unless Q 0 8Upplemented.by other dust catcning means. (2) Screens without viscous- <:oated surfaces: in theses the screening effect is augmented by the action of the viscous—coated surfaces against which most of the dust impi.3es and 5-8 caught. It is on these c0mbined principles that steel-wool filter wOrks. In a cloth filter, the cleaning effect is due to screening action, aridnatural viscosity of the fibre and the peculiar ability of the nap to cetchand‘bind fine dust particles. (3) The settling of dust in air Chiflfibers; dust contained in air at rest will settle if given enough time. If the air is in motion but at low velocity, some of the dust Will settle. It is this principle which is u ilized in moet cleaners having air chambers. Often the air entering such a chamber will assume a whirling motion motion by means of which some dust will be thrown against the walls and be caught. (4) Separating the dust particles from the air by adding weights to them: this is partly what happens in a water spray washer. The dust particles whiCh can be wetted by water can easily be caught, but those which cannot will manage to get thnough, as is the case with fine particles of carbon dust. '(5) Impinging against viscous- c0ated surfaces: viscous«coated surfaces will bind any dust particles Which come into immediate contact with them. Tocause this immeiia e contact, the air current must be divided into narrow streams or thin Sheaves and these must strike the viscous-coated surfaces at a high velocity in order that the dust particles may break thvough the air cushions which tend to xprevent the close contact. By causing the air cunrents to make numerous ‘turns they are forced into contact with a large viscous-coated.area, at levery point of which some dust is caught. In utilizing this principle of air'cleaning it is very important that ample air chambers and other Open Spaces are provided in which the dust may build up and accumulate, without Shutting off the air passages and.thus cause the resistance to increase. The catching of dust by the wetted eliminator plates of an air washer is also based.on the above principle. TYPES OF AIR GEARS: Wires screens of fine mesh have been used as air filters. Dust particles which are larger than the free Openirg of the individual meshes are held back and those which are smaller pass through. Some of the dust particles are of such size that they are actually caught in the mesh openings and stay there, being wedged in between the wires. Even the finest wire screen has a very low efficiency for catching atmospheric dust. A fine wits screen soon clogs up and during this process the filter resistance increases rapidly. 1.'.'hen all meshes have been filled no air can pass through this screen. It is difficult to thoroughly clean a wire screen which has been plugged with dust particles becuase these are locked or wedged in between the wires. If a filter is made up of several screens placed behind one another its dust catching efficiency Will increase somewhat, but it will c10g up Just as quickly and the difficulty of cleaning the filter will, of course, be greater. Few,if any,engineers use wire screen 3 as air filters nowadays, but their Charachteristics are well worth studying because the same principles of Catching the dust are being utilized in the steel wool filter. I Cloth Filters: This is the oldest type of air cleaner. Various Weaves and weights of cloth have been used, but so-called cheese cloth 5-8 probably the most common in building ventilation. The average velocity at which the air is drawn through these cheese cloth is probably about thirty feet per minute, althOugh some engineers Specify a lower and others again a higher velocity. This corresponds to about thirty-three sqmire feet of Chee Se cloth per one thousand cubic feet of air per minute. Cheese cloth is an improvement over the wire screen filter, because even the smoothest cloth has a fine nap which is an efficient dust catcher. Otheriise the cheese cloth works on the same principle as a wire screen, in that most of the d75t is caught in the meshes of the cloth, the balance being csught and held by the surface nap. .A prominent consulting engineer, who has had extensive experience with cloth screens, said that cheese cloth is not suitable for catching carbon dust, because this kind of dust cannot be removed when cleaning the filter. This is a decided disadvantage because even in a city using hard coal exclusively, such as New York, eighty per cent of the atmospheric dust consists of carbon. The friction of the passing air, which is considerable, the cutting action of the sharp edged dust particles as well as their wedging and stretching action, the effects of brushing and beating the cheese cloth screens for the purpose of cleaning them, and their deterioration due to moisture in the air are all factors Which combine to quickly destroy a cheese cloth filter. Under average conditions the useful life of the cheese cloth itself will probably notnnxceed three years. Cheese cloth screens are now being rapidly superseded by air washers and viscous— coated.metal or composition air filters. Any engineer who will take the trouble to estimate the cost of cheese cloth filters over a period of twenty to thirty years, giving due consideration to space occupied, re- newals, cost of cleaning and.repairing, compound interest On the capital invested and on the c0st of maintenance, Will find that they are among the mOSt expensive of air cleaners. AIR "AShEES Lo attempt will be made here to go into the characteristics of the many special types and.aahes of air washers on the market. If an architect merely specifies air washers of certain capacityes without going into a detailed description of what he wants, the contractor will generally furnish the cheapest apparatus he can buy or build in his shOp. The bulk of the air washers used in buila Jag ventilation are selected in tr is manner and it is to these that the following can eats refer. An air washer for 50,000 C.F.h. measures about 10‘ x 10' x 9'. The amount of water used for its Operation is about two gallons per min. plus six hundred 3 “110 s every week for cleaning, etc. The power cOn.- mption for its Operation is about 0.2 to .15 H. P. per 1,000 c.r.x. A ir washers are used for their cooling effect on warm days, for humidifying he air and for cleaning it. In building ventilation, it is particularly in theatres and other places of public assembly, et6., that air washers have been used for their cooling effect. Unfortunately the washer introduces much excess humidity which very often over-balances the cooling effect, so that the patrons of a theatre, for instance, feel more uncomfortable with, han without the waSher. There are numerous industrial processes requiring humidification, but it is doubtfu vrether it is actually needed or even desirable in the average building ventilation. Both in the ventilation Of buildings and of electrical equipment (turbo generators, etc.,) air washers have been used primarily as air cleaners as t1 e name indicates. Their cleaning efficiency is higher than tizat of cheese-cloth screens, as Operated in the average installation, namely, with neglect ul attendance. As there is nothing to clOg or shut of the air passages, air washers Operate with a prattically constant resistance. Fine carbon dust repulses water in somewhat the same manner as particles Of grease and oil, although to a less extent, and far this kind of dust, therefore, air washers are not efficient. On page 355 Of the May, 1921 issue of the Journal Of the.£.S.H.V.E., the following statement by a prominent air-conditioning engineer is given: - ”In the processing of certain materials it is essential that particles of every description be removed from the air. It is a well-known fact that spray type air washers will eliminate only about fifty per cent of the carbon particles from the air, which necessitates the employment of some other method of dust removal." In industrial sections all atmospheric dust, whether it consists of carbon or not, is more or less greasy and sticky on the sur- face and is therefore little susceptible to the spray of an air washer. There is no reason Why a well built air washer of non-corrosive metal should not last for a long time, say twenty to thirty years. Being constantly eXpOsed to moisture and air, the life of a steel washer, however, is much shorter - only five to seven years. An air washer is a fairly complicated and sensitive piece of machinery and it therefore needs skilled attendance. This fact rather than any fault in principle is probably the reason that so many air washer installations are neglested.and not Operated. It is not advisable to use air washers without h nidity control in buildings having fixtures, decorations or merchandise diSplays which are susceptible to damage by moisture, such as safe deposit vaults, museums, libraries, are collections, hotels, theatres and stores. On account of their water and.power consumption, air washers are by far the most expensive air cleaners in existence. CE‘ET'TELIE‘LGAL CHESS One of the most common methods of separating the dust and other materials from the air is to pass the mixture through a centrifugal or cyclone collector. In this type of collector the mixture of air and material is introduced on a tangent, near the cylindrical top of the collector, and.the whirling motion sets up a centrifugal action causing the comparatively heavy materials suspended in the air to be thrown against the side of the separator, from which position it spirals down to the tail piece, while the air escapes through the stack at the center of the collector. For most systems, the inlet size of the collector may be the same as the diameter in inches of the main pipe leading to it. The larger the collector, within certain limits, the better will be the separation, and the less will be the back pressure on the fan and.the power consumed. Special construction is sometimes required for fine dust, also some blow-pipe manufacturers use a special type of collector for furnace feed, the object being to deliver the material to furnaces as uniformly as possible. When more than one fan delivers into a single collector a back pressure valve is required to prevent one fan blowing back through the other in case the second fan should st0p . for any reason. TEEL'WOOL FILTERS Viscous-coated filters made with steel wool or split wire work On the principle of the fine wire mesh, but with the distinct additional advantage that all surfaces with which the passing air comes in contact, have a viscous coating which also binds some of those dust particles which are not caught through the screening action of the steel wool. Such filters also have innumerable dead air Spaces in.which the dust accumulates, although in a Steel wool filter these air spaces are naturally very minute. The dust catching efficiency of these filters is higher than that of dry Wire screens, neglected cheese-cloth filters and air washers. If the steel wool is firmly packed into the boxes (filter cells) so that the air passages are very small, only the finest dust particles can escape being caught. Their dust binding efficiency is therefore sufficiently high for most practical purposes, such as general ventilating work and the like. .A steel wool filter may be considered as a series of fine wire screens placed immediately behind one another. Most of the dust is caught on the front surface, or say in the first half inch of the steel wool body, whereas a small percentage of it is carried farther back into the steel wool. On account of the unfavorable dust distribution and because the v0ids available for dust accumulation are so small, the resistance of the filter rises very rapidly with increasing dust accumu- lation. The resistance of a steel wool filter is very low in a clean state, but when the dust accumulation approaches its maximum capacity the resistance becomes quite excessive. Viscous metal filters are cleaned periodically by washing the filter cell as a whole in warm water and soda. In submerging a dirty steel wool filter cell into the tater some of the dust flows off, but some of it is forced deeper back into the steel wool by'the action of the water. It is then ahmost impossible to remove it on account of the dust particles becoming locked.or Janmed.in.between the steel wool strands - or because it is accumulated in enclosed air pockets. IBecause of this condition, this type of filter will rarely go back to its original resistance after being washed, and with subsequent washing Opera- tions the resistance will continue to grow. By using several grades of steel wool (of Vayying coarseness) in a filter cell and by arranging it in successive layers so that the coarsest grade is in the front part and.the finest grade in the rear part of the of the filter, its dust accumulating capacity'may pOssible be increased somewhat. The more dust that is accumulated in the filter, however, and the deeper into the steel wool body the bulk of it penetrates, the harder it will be to remove it by any known cleaning or washing process. The benefits to be derived from any such zoning of the steel wool are, therefore, problematical. The other class of vidcous—coated metal filter has its cell filled with a number of specially perforated and corrugated metal sheets with air spaces between them. The perforations are so large that no dust particles can be caught in them and their sole object is to split the air into thin sheaves, Which strike the viscous-coated surfaces behind the perforations at high velocity and in such a manner that practically all of the dust particles in the sheaves impinge and.are caught by the viscous-coated surfaces. The air spaces between the successive metal sheets are more than ample to enable the dust to build up and accumulate without serhously cutting down the air passages and consequently the filter resistance is not appreciably increased. There being no screening action in the filter and all dust accumulations being easily accessible to the washing water, the filters are easy to clean and will invariably go back to their original resistance, after eadh washing. This same principle of catching dust through impinging against viscous-coated surfaces is also being used ex- tensively today in throw-away filters. Instead of being made of metal throw-away filters are made of a composition material similar to cardboard (they some times have a metal case which is not thrown away) which makes them very inexpensive, and when they become dirty enough so that they are inneficient or the resistance becomes objectionable high the whole filter is thrown away and replaced with a new one. Some manufacturers make a viscous—coated steel wool or glass wool throw-away type filter. iost filters used in domestic work today are of this type. SELF Clash HG FILTERS One type of automatic (cleaning) air filter is the so called "c0nstant effect" air filter. It is an endless screen hung on a sprocket Which is moved at intervals by'means of a small motor (See Fig. 2). The drive rotates the t0p sprockets, moving the screen about one-sixth of its length once each working day, thereby completely rotating the screen every six days. This filter exerts a two stage cleaning action; as the air passes through the first and second sections of the filter, it is thoroughly filteres, each part thereof receiving an equivalent filtering effect. Tests have established the fact that under average conditions the filtering effectiveness of the ViSCOHrCOated surfaces increases slightly, but prOgressively, from the moment of coat— ing with fresh Viscosine until the end of the sixth day, at which time the effectiveness of the surface began to diminish. The gain in effectiveness from the first to the end of the sixth day is due, apparently, to the in- creasing accumulation of the dust particles in the viscous film, the effect of the film as a dust collector being improved by the presence of the pre- viously collected particles themselves, until the end of the sixth day, when the film.may be said to be approaching saturation with dust, and therefore less effective for the collection of additional dust. a q a zfimtw m2 :3me m2 :3me m2 2. >3 :3 2. >3 Em 2. >3 :5 VvVVVvVVVvV vvvvvavvvvarvv wVVVwVVVvVVVwVV J. uo3 0mm 2. >49 ozw .z. 55 en. n n n Referrirg to-the diagram, it is at once apparent that the method of moving the screen intermittently, at definitely established intervals, provided balanced filtering effectiveness, inasmuch as the lesser effectiveness of the freshly coated section of the screen emerging from the viscosine bath is equalized by the increased effectiveness of the Opposite section of the screen , which is in the condition of maximum effectiveness Occur- ing on the sixth service day. This cleaning of the screen plates, in the viscosine bath, is an interesting phenomenon. The dust wh‘ch the filter collects is held entirely in the viscous film. It does not adhere to the surfaces of the screen, but is suspended freely in the viscous film, retained by the cohesiveness of the fluid. When the dust-laden film is immersed in the fluid bath, the film befomes a part of the body of the liquid, ceasirr to exist as a film, and.the dust particles are free to move within the entire body of the liquid. Being heavier than the liquid, they immediately sink, leaving the surfaces of the screen absolutely clean. ELECTRICAI.PRECIPI-ATICi METHOD The cottrell method of prezipitation dust and other material particles from fumes and.amoke by the appliCation of high-voltage, unidirectional current has been in commercial use for some time. The process consists fundamentally of passing the dust~laden gas between two a positely charged electrodes, one, of small arc, known as the"discharge electrOde“, and the other, of larger area, called the “collecting electrode". Under preper conditions the dust will be precipitated from the gas, upon the surface of the collecting electrode. The discharge electrode is insulated from the treeter and ground, and is connected to a source of high voltage, unidirection- al current. The collection electrode is grounded, For preper results, the discharge electrode should be of negative polarity and the collecting electrode of positive polarity. The form of the precipitator or "treaterh may be designed accord'g; to the type of the collecting electrode, which may be pipes, plates, screens, etc. The two principal forms are the "wipe“ and “plate" types. The most simple form of precipitation consists of a metalic pipe, from 5" to 18“ in diameter and 10' to 20‘ in length, with a wire or chaun stretched along the center of the pipe, insulated from it and ground. The gas to be treated is passed through this pipe at a velocity of frqn five to ten ft./sec. while a unidirection81 potential difference of from 25,000 to 100,000 volts is applied between the wire and the pipe. The voltage is dsually maintained above that which will produce corona on the central wire, but below that which.will cause frequent arcs between the wire and the pipe. As the gas passes through the tube, the majority of the material particles whichpir carries acquire a charge of a polarity similar to that of the discharge electrode, are repelled from it, and attracted to the pipe or collecting electrode and precipitated on its walls. .A small quantity of the particles become charged with the same polsrity as the pipe and is deposited on the central wirl, or chain. A t intervals, the precipitated material is removed from the pipes by rapping them with a system of hand or motor Operated.h.mmers. The dust falls from the pipes and is collected in a hOpper beneath them. During the cleaning Operation, which requires only a few minutes, the flow of gas through the section of pipes being cleaned is stOpped by shunting the gas through other sections or flues. In practice, a treater of this form 'usuelly consists of a number of pipes in multiple, he number depending upon the volume of gas to be handled. Another class of precipitator, known as the "box" or “plate” type, is SOmetimes used. This consists Of a rectangular chamber in which are placed flat, sheet metal collecting electrodes, with.wire or chain dis- charge electrodes suspended between them. In$some recent installations, concrete collecting electrodes are used. The high-voltage, unidirectional current if usually obtained by trans- forming a low—voltage, single«pgase alternating current to the desired high voltage, and then rectifying. In the majority of installations up to the present time, the rectifier xx used is of the "leap sWitch", or mechanical—c smutator type, driven either fran the motor-generator shafe or by a separate synchronous motor, This latter arrangement is used.almost entirely in recent practice. Recently the development of the kenotron, or hot-cathode sacuum.tuhe has provided a rectifier which has no rotating parts, is noiseless in Operation, and gives a unidirectional current and coltage wave superior to that obtained from.the mechanical type. Some precipitator equipments using the kenotnon type of rectifiers are now in Operation or being installed. The mechanical type of rectifier, with separate driving motor, cOnr sists of four arms spaced 90 degrees apart, with conducting tips placed on the ends of the arms. The revolving arms are supQOsted on an extended shaft Of the motor-generator or motor, which is especially designed for thbs purpose. The synchronous motor for driving the rectifier must have four poles. The kenotron rectifier depends for its Operation as a rectifier on the fact that when two electrodes, one of which can be heated, are placed ina container exhausted to a high drgree of vacuum, current can flow through the space separating them only when the heated electrode is negative. A constant voltage, the amount of current that can be rectified by such a device increases rapidly with the temperature of the heated electrode (up to a limiting value), but remains constant as long as the temperature of the latter does not change. Considering the fact that a kenotron conducts in one direction only, it follows that, when placed in an alternating- current curcuit, it rectifies this current, that is, it causes it to become unidirectional and pulsating by allowing current to pass during one half wave and suppressing it during the next. Using two 9r four kenotrons in suitable circuits, both half waves can be rectified to Obtain unidirectional current. When a kenotron is passing current (the anode being positive), the pOtential drop from anode to cathode may be from 100 to 1500 volts or more, depending upon the design Of the tube. During the next, or reverse, half wave no current flows (the anode being negative) and the potential drOp across the tube may be several thousand volts. In general, this reverse «otential drOp equals the peak voltage of the alternating source plus a voltage due to the capacity of the load. .As the peakanf the tran former voltage for the unused half wave is higher than it is for the useful, and as practically every load carried by kenotrons has a capacity which becomes charged during the usefull half wave and adds its potential to the inverse of the high-tension source during the next half wave, the sum of the inverse and.capacity voltages is usually very large and is the greatest voltage stress to which a tube is subjected, With the possible exception of surges. The amount of this inverse voltage is one of the Largest factors giverning the selection of a particular tube. In the construction of a kenotron, as shown in Figure 3, the electrodes are supported inside a highly evacuated glass bulb. 6A 5E ”3.9/2 2””- 1/ APPROX. 2"DIA. / APMX. 6A 55 *370/ —-~ OUTLINE Kc-gadflrtmrm 157.5 The anode, or positive electrode, consists of a cylinder, or disk, of molybdenum. While the cathode, or negative electrode, is a suitable length of tungsten wire formed into 100ps. The filament terminals are attached to a base which furnishes an easy means of mounting the kenotron for service. The anode terminal is brought out from the end Opposite the.filamentiterminals through.a cap base. The energy required to heat the filament to the prOper Operating temperature is usually obtained from an auxiliary filament transformer. It is evident that if only one kenotron is used, only one half of the applied alternating current wave can be rectified; that is, during alternate half cycles, the current value will be zero, with correSpondingly low average output for apparatus of a given maximum capacity. By utilizing two kenotrons and.a transform- er with a middle trap in its high—veltage winding, both.ha1f wavws can be rectified, nut the transformer is still being worked irsufficiently, as lthe maximum value of the rectified voltage will be equal enly to the m ximum voltage across one-half of the transformer winding. This means that to obtain an example 85,000 valts, direct current, the transformer must be designed for an alternating cur:ent voltage of 100,000 maximum, or approximately 71,000 effective. However, with a cmbination of four kenotrons it is possible to rectify both half waves and to utilize the full maximum value of the alternating current voltage. It is recommended, therefore, to use four kenotrons for each rectifiying unit; A unit of four K C ~I hanotrons has a capacity of 500 milli—amperes, direct current, at a maximum voltage of 100,000, correSponding to an effective value of about 71,000 volts, alternating current, that is, four kenotrons will rectify about thirty kilowatts. If greater capacity is required, it can be obtained by connecting addutional units of four tubes in mmltiple with the first set. For later capacities, other kenotrons are available. The efficiency of the ‘kenotrons is high, as the voltage drOp between anode and cathode is about 500 - 1500 volts, while the energy required for heating the filament is less than 500 watts per tube. The life of the kenotron, barring mechanical injury, like that of the incandescent lamp, on the life of the filament, this life constantly being improved by continuous experimental and develOpmental work. Data at present available indicate an average life of about 3000 hours, with every prospect of a substantial betterment of this figure. In this connection it should be observed that in order to obtain the maximum filament life, its heating current should.be drawn from a current which has a maximum voltage variation of not more than 2% from the average value. The rectified current wave obtained from the kenotrons is much smoother and.more uniform than that from the medhanical restifier. while the principals installations of Cottrell precipitators treat fumes from ore-smelting furnaces for the recovery of metal values, or gases from cement kilns to Obtain the potash contained therein, or to precipitate acid mists, pther applications of the process are very numerous. For instance, it has been used in precipitating coal s oke; in the pro- duction of dried.powered foods, such as powdered milk and eggs; in the removal of tar from illuminating gas; in the placing of sane in the proper proportion on sand—paper; in the cleaning of hot blast furnace gases, etc. In gases cantaining elements of different volatilization temperatures, fractional precipitation is possible; the elem.nt having the higher tem- erature of volatilization is precipitated first, while he temperature of the fume is high enough so that the other elements are in a gaseous state. The temperature is then lowered, and the remaining constituents precipitated. The size and type of an installation depend on the volume and character of the gas tp be treated and the requirements of location of the treater, It is therefore necessary in determining the type of treater to be recmnnended for a specific installation, to know the volume, temperature, and'character of the gases to be treated, and type of pparatus producing these gases, the physical arrangement of the flues, nd the electric power supply available at the location of the instalLation. In connectioriwith the electrical precipitation method of filtering air it is desirable to know something about ionization of air and its functions. Intensive investigations have until recently failed to disCOVer the specific cause of deadness, or lake of a stimulating quality, in the air of occupied rooms, even when tempneture and.humidity are controlled, as contr sted.with the air of the open country. Preponents of the Open air treatment ascribe this quality of freshness to a viaal principle which is lost when air is brought indoors, particularly when ventilation is effected by mechanical means. In recent years, since the carbon dioxide, oxygen, and crowd poison theories have become obsolete, ionization has been arreested as the air soluble vitamin. Accor to Hess , all gases, like electrolytes, con ain mo itively and neg atively charged ceu riers of electrici y, e.g, atone, molecules, or molecular groups, which are called ions. The -lO charge carried by an ion is the el mentary charge; nanely, 4.77 x 10 electrostatic Ullits (3.8. U.). It is believed ti.at this char 5e is the same in all gases and that it is equal to that carried by the hydrogen ion in the electrolysis of liquids. Becuase of this charge, ions move under the influence of an electric field.and.the direction w. ch they talce depends upon th e sign of their harge. In general, two clases of ior s are recognized; the small or molecular size, and the larger or Iengevin ions. Owing to this difference in size, the speed which the two classes of ions attain in an electric field differs enormously. The mobility of small ions in ordinary air varies from 1 to 2 cm per second in a field of unit intensity (1 volt per centimeter), and ti ‘.e mobility of the large ions varies from .01 to .00 J05 pm per second, depending Upon their size. As a general rule, the mobility of negative ions is someWhat higher than that of positive ions. Large ions are forn ed‘by arglomer a tion of small positive or neg: Mt ve ions wi th condensation nuclei, such as dust, fuxnes, sznokes, or drOps of water. -ney are present in great numbers in city air which is polluted with prod d“"ts of combustion from chimneys and from autohobile gases. Under such conditions the number of small ions is at a minimum, and it varies inversely wi hi the number of large ions. Between the small and the large ions are the so called intermediate ions, which are formed under certain conditiOns of humidity. Their mobility varies from about .1 to .01 cm. per second in a unit field. Although this classification is generally adhered to experiments show that gaseous ions do not occur predmninately in anynwel-defined sizes, but that there is a con- tinuous distribution of sizes fran the very small to the very large. The freQuency of distribution seems to depend largely on weather cor- ditions and on the extent of atmospheric pollution. In nature, ions are produced by solar ratiation, by cosmic rays, and.by radioactive changes in the soils of the earth. Strengly ionized gases diffuse through the capillaries of the soil by the asgirating action of the wind and when the barometric pressure falls. It is believed that this soil respiration contributes about 60% of the total ionis content of the air near the surface of the earth. The state of atmospheric ionization is maintained, more or ledd, by the simultaneous actions of other natural processes which tend to destroy or to neutralize the ions. The most important of these are (l) recombinations of ions of Opposite charge to form neutral ions, (2) agglomeration with condensation nuclei to form large ions, and (3) diffusion and adsorption by solid or liquid conductors. The number of positive and negative ions in a unit volume of air is usually counted by means of an apparatus devised by Ebert. Figure 4 shows the modified form of this apparatus. A stream of air is drawn by fan suction through a cylindrical condenser, the central rod of which is charged to a known potential with a polarity Opposite to that of the ions to be counted. The charged rod is well insulated and it is con- nected to the quartz fibers of an electrometer. All other parts of the apparatus are grounded. As the air passes down the condenser tube, ions of Opposite sign are attracted to the rod, and upon striking ti attract a quantity of charge equal to their own. Only those ions will reach the charged rod which have sufficient velocity to carry them across the intervening space before they are carried away by the air stream. From the rate of dis— charge of the electrometer and the rate of air flow - the latter measured by an orifice meter - the number of ions per unit volume of air can.be c0mputed. . If’ni'is the number of positive or negative ions in a cubic centi- meter of air,uJ the volume of air passed.theou§h the condenser, U5 the initial charge in colts,\4 the final charge, corrected for natural leakage if any, 8 the charge carried by an ion (4.77 X (0 -10 E. 5.6% ), and C; the combined electrical capacity of the condensed and the electro- meter in E.S.U., the following equation will hsld: C U -U, _ _ C(U°-U‘) (h1)eo»=.¥;§3,2 AHJ H+—"3ooecu The division by 800 gives the loss of potential in E.S.U., that is, one E.S.U. of potential equals 300 volts. The value of544-is obtained by charging the system negatively, and hat ome-by a positive charge. Usually it takes five minutes to make an observation. Less time is réiuired When the ionic content is unusually high. Under the supervision of the A.S.H. & v.3. a series of experiments was carried.omt in rooms, both occupied and unoccupied (1) with no ventilation, (2) with Window—gravity ventilation, and (3) with mechanical ventilation, in order to determine the extent to which the number of small ions is effected'by respiration and transpiration, and by mOdern air-conditioning methods. ' gig-‘- In contrast with the prevailing belief, the ionis content in unoccupied heated rooms did not siffer much from that out of doors, and in COld weather it was often'higher, owing probably to a temperature effect. In Occupied rooms there was a marked decrease in both positive and negative ions. Immediately after the occupants assembled, the ionic content of the air fell abruptly to a very low value, which was maintained until the occuxants left the room. Both positive and negative ions began to rise again as soon as the peOple departed. The mimimum su ply of outdoor air required to maintain normal ionic content in a crowded room was found to be prohibitively high, (160 C.E.M. oer person). With the usual air supply of 30 C.F.M. per person, the ionic content did not seem to differ greatly from that with no ventilation at all. On the other hand, it was possible by means of artificial ion- ization to control both the quantity ahd the quality of ions at any de- sired concentration up to 10,000 ions per cubic centimeter, with or with- out ventilation. Mehancial ventilation reduced the ionic content from 0% to 30%‘by diffusion and adsorption to metal conductors. Heating the air by means of a central air system increased the ionic content, and cooling by similar methods decreased it. The usual methods of washing, humidifying, or dehumidifying by means of water Sprays, deprived the air of all small ions, and produced.a great number of large negative ions, or condensation nuclei, bu the Well known Lenard effect. Recirculation reduced.both positive and negative ions by diffusion and adsorption to metal conductors. This and.0ther experiments on artificial ionization indiCete that it is fairly practicable to control the ionic content is occupied rooms at any desirable level. up to a maximum.of 10,000 ions per cubic centimeter, without producing a perceptible quantity of Ozone. According to the physiolOgic experiments it is dOubtful whether a concentration higher than 2,000 ions would be needed in ventilation works, and experiments are now in pregress to determine the threshold value. The influence of ionized.air (small ions) upon total metabolism, respiration, pulse rate, blood pressure, and body temperature, was studied on human subjects lying on cots (a) under basal conditions, (b) two to four hours after breakfast, and (c) three to five hOurs after a light lunch. .A group of sixty persOns in a total of one hundred forty-one experiments were exposed for a period of one hour or more to air containing from 5,000 to 1,500,000 ions per cubic centimeter (normal air contains fron 50 to 800 small ions per cubic centimeter), after a preliminary restint periOd of one to two hours in normal air. under the experimental conditions ionized air appeared to ecert a normaiizing influence upon the organism by accelerating the physiologic processes in instances in which these processes were below the normal range of the majority of subjects, and reversely, by decreasing the physiologic activity in cases in which the functions were above the normal range. Folowing the ionization period there was a reversion of the functions toward their steady state prior to the ionization period. This indication, being of a somewhatsurprising nature, requires verification by further experiments. AlthOugh the physiologic response to p0sitive and negative ions did nOt seem to differ greatly, certain differences were observed in the sensations produced by the two kinds of ions; positive ionization resulted.in headaches and irritation in the nose and throat in some cases, whereas negative ionization predisposed to relaxation and other sensations of a desirable character. In a few instances these effects were discernable a few minutes after turning on the ionizer. LEWLIEZ'CES CCI'CEZL :70 THIS SUBJEC PhysiOIOgic Changes During Exposure to Ionized.Air - by Yaglon, Brandt & Benjamin - H.P. & A.C. — 1953. Changes in Ionic Content of Air in Occupied Rooms Ventilated by Natural and Mechanical Lethods - by Yaglen, Benfl anin & Ghosts,- H.P. & A.C. October 19 31. Electrical Conductivity of the A tmosphere and its Causes - Hess. 4r ,Air pollution from the Engineer's Standpoint - by H. B. Heller, Pittsburg, Pa. from H.P. & A.C. Jan. 1931. Methods of Cleaning.A tmospheric.A ir — by.A. K. Goodloe.A. S.H. & v.3. .A ir Dust - Chapter II of A. 0.2. HandbOOk. The Electrical Precipitation of Susyended Hatter in Gases, Journ. Franklin Instutute, Sept. 1912. Theory of the Removal of SuSpended.Matter from Gases, Journ. Ind. and Eng. Chemistry, Oct. 1913. Electrical Precipitation.by E. G. Cottre11.Introd ctory address delivered at the 8rd lidrwinter convention of the Ameri ce.n Institute of Electrical Eneineers, Lew York, Feb.19, 1915. Electrostatic Precipitation'by O. H. Escholz, Research Engineer, Westinghouse Elec. & Mfg. 00., East Pittsburg, Pa. — A. I. E.E. Sept. 1? 1C, 0 The Electrical Precipitation of Suspended Particles,by F. G. Cottrell. Journ. Ind. and Eng. Chemistry, A ugust 1911, page 542. Bulletin 202 issued by Researdh Corporation, 25 fiest 43rd st., flew Yorkm on the Cottrell Processes of Elecgrical Precipitation. Bulletin 201 for the Removal of Ash and Flue Dust in Powdered.Fuel Plants, issued by the same company. Recent Conclusions Pe1t tair n3 to Electrical Precipitation, by Walter A. Schmidt. Journ. America n Institution of Elect rice 1 Engineers, L-.u;t1st 19:32, p113e 802. Bulletin 20 4 is:ued.by tie Research Corporation for Cleanins Hot L Q ('1, Ga Electrical Pre ecipitation ~ Its tb eory and application at the International Smelting Company's plant, Liami, Arizona, by R. J. Kerns, piiolished.by the Ele MC ric Journal. trical Precipitation Electrical Errineering Features of the 31 c O: rn. mnerican Institute P Process, by x. H. Horne, published bu of Electrical Engineers in agust 1922, '3’... I: . 'J // 1’ A; ‘ ,1, -. U"?~- _ ;1‘ l ‘0‘. 3' 5", ‘--'-:~r: