INVESTIGATION OF ATMOSPHERIC POLLUTION 113 REPORT. Committee for the Investigation of Atmospheric Pollution. First Report: April, 1914, to March, 1915. (Lancet SuppZ., 1916, February 26, pp. i. to XI.)-The Committee consists of C. J. P. Cave, J. G. Clark, J. €3. Cohen, H. A. Des Voeux, W. L. Hawkesley, J. B. C. Kershaw, R. Lessing, J. S. Owens, E. J. Russell, Sir N, Shaw, E. D. Simon, W. Smith, and F.J. W. Whipple. I t was appointed ‘‘ to draw up details of a standard apparatus for the measurement of soot and dust and standard methods for its use.” For the purpose of this investigation, the question of variations of the normal gaseous constituents of the atmosphere is ignored and the interpretation of the term (‘ pollution,” adopted by the Committee, relates to such matter, solid, liquid, or gaseous, as reaches the surface of the earth or falls upon the buildings, etc., either by its own gravity or with the assistance of falling rain.As a preiiminary step an analysis was made of a specimen of the grosser solid pollution, in the form of suspended particles, intercepted by the ventilator filters of a large institution in London. The analysis showed : Sodium chloride, trace ; calcium carbonate, 2.17 per cent.; ferric oxide, 2.44 ; calcium sulphate, 5.09 ; alumina, 8-34 ; magnesium carbonate, 0.33; sand, 37.99; carbon, 35.48; ammonium sulphate, 5.77 ; tar (extracted by carbon disulphide), 1.49 ; and fibrous matter, 0.95 per cent. I t is evident that the two main sources of pollution areearthy matters from the surface of the land and the products of imperfect combustion of coal.In connection with the latter, analyses were made of samples of soot deposited in chimneys in use with ordinary domestic hearths. These samples showed a large proportion of matter soluble in ether (tar), about 6 per cent. of combined sulphuric anhydride, and 4 per cent. of combined ammonia. I t is noted that, whereas a considerable proportion of the sulphur of coal is discharged in the form of sulphuretted hydrogen and the oxides of sulphur in gaseous form, and whereas the ammonia may also rank as gaseous pollution, yet these constituents are foundunited in the form of ammonium sulphate, which as a solid and in solution comes prominently within the scope of this investigation.Among the constituents of smoke, the vapours of tarry hydrocarbons play an important part in condensing on the solid particles of carbon and imparting to these an extraordinary power of adhesion and resistance to the cleansing action of rain.Methods of Work.-The objects to be attained in the course of the inquiry were formulated as follows : (a) To measure the amount of matter deposited from the air on a given area at any place during a fixed period.(b) To measure the amount of impurity held in suspension in the air at any time and place. (c) To find the nature and composition of the deposited or suspended matter. On consideration, it was114 REPORT recognised, however, that no single method could afford a simultaneous solution of problems (a) and ( b ) , and since the method of measuring the amount of deposited impurity was capable of easy development, it was decided to put this into operation first, leaving the measurement of suspended impurity to a later stage of the inquiry.Nevertheless, a certain amount of preliminary investigation has been carried out on the latter problem, and some nine possible methods of procedure have been more or less thoroughly examined.The method of filtration through cotton- or asbestos-wool presents difficulties in connection with the accuracy of weighing the deposit on the filter and its quantitative detachment for analysis. Aitken’s dust-counting method is interesting, but hardly suitable, as it affords no measure of the size and weight of the various particles nor of their composition.Optical methods, based on measurements of the opacity of a column of air or of a glass plate coated with a sticky substance, on which a jet of air is caused to impinge for a short time, might be capable of development, and a method of this order has been under investigation by J. S. Owens with some measure of success. The apparatus used consists of two bottles serving as aspirators ; water, allowed to syphon from one to the other, draws a measured volume of air through a disc of filter-paper of standard area, the discoloration of which is compared with a scale of shades.An observation can be taken inabout ten minutes, and the instrument has been approved by the Committee for the measurement of suspended impurity. The major portion of the present report is concerned with the measurement of the deposited impurities, including those precipitated by the rainfall.A standard gauge has bean devised and distributed in many of the large industrial centres of the kingdom, where sygtematic observations and records have been carried out during the period under review. The standard gauge consists of a galvanised iron stand sup- porting a circular enamelled iron gauge vessel of 4 square feet collecting area.Pro- jecting upwards and outwards above the edge of the vessel is a wire screen, open at the top, to prevent birds from settling on the edge of the vessel and contaminating the contents. The vessel has a conical bottom communicating by a glass tube and rubber connexion with a group of three or more bottles connected together, capable of holding one month’s rainfall.The rain and solid matters falling on the gauge aiea are collected in the bottles and removed once a month for analysis. The gauges are to be placed, if possible, on the ground level in open spaces free from abnormal dust. Before removing the bottles containing the water and deposit, the gauge vessel is to be washed down with some of the collected water, using a brush and squeegee of standard pattern (supplied with the instrument) to remove any adherent matter.Analyses are to be made (generally by the local Public Analyst) according to a, uniform scheme briefly outlined below. The bottles are to be allowed to remain at rest in the laborstory for several days until the contents are completely settled; the approximate volume of contents should be noted at the time of receipt.Undissolved Mutter.-The whole of the amount collected should be used for the estimation. The filtration is best done in the following manner : A syphon-tube is inserted in the bottle to within about 1 inch from the bottom and the bottle placed at a convenient height for control of the discharge. The suspended matter is collected in a Gooch crucible supported in a graduated bottle, at least as large a8 the station bottle, and connected with a suction-pump.The filter-bed is prepared fromINVESTIGATION OF ATMOSPHERIC POLLUTION 115 a tared filter-paper, 12.5 em. in diameter, which is heated with about 200 C.C. of the sample water, specially syphoned off for the purpose. The paper is shaken violently with the water in a flask until reduced to a pulp, a portion of which is collected in the Gooch crucible to form a filter, and the rest reserved.Filtration of the sample is then proceeded with, the clear liquid being syphoned first. Should the filter become clogged, it should be sucked dry and removed together with the collected deposit, and a fresh bed prepared.Towards the end, the contents of the bottle are shaken up and poured on the filter, the bottle being rinsed out with some of the filtrate. Any of the paper pulp left over or previously removed is finally placed on the top of the matter collected in the crucible. If there be more than one station bottle, it is best to filter the clear liquid of all before collecting the sediment of any.The contents of the Gooch crucible are washed, dried at 105' C., and weighed. Tarry Matter.-The crucible is placed in an extraction apparatus and extracted with carbon disulphide ; the difference found after drying represents tarry matter. Ash.-The residue is carefully ignited, loss of particles through the perforations being avoided. Dissolved Matter-250 C.C. of the filtrate are evaporated to dryness for estima- tion of total solids, and the residue is gently ignited.One litre is concentrated, acidified, and treated with barium chloride; sulphates are expressed as SO,. Chlorides are estimated as GI by titration of 500 C.C. with TT silver nitrate. -4rnmonia is estimated by slightly acidifying 1 litre with sulphuric acid, concentrating to 100 C.C.and distilling from alkali; alternatively 10 to 25 C.C. of the water may be treated with 1 C.C. of Nessler solution. Lime is estimated in 1 litre, after addingammonium oxalate and ammonia and concentrating to 100 C.C. Alkalinity or acidity, expressed as H,SO, or NH,, is estimated in 500 C.C. by titration with & solutions in presence of methyl orange. All results are expressed as per cent.of total solids, and calcu- lated as metric tons per square kilometre. Classi$cntion aud Discussion of Results.-Full results for the six months, from October, 1914, to March, 1915, have been returned from twenty-five of the thirty- nine recording stations, and are reproduced in the form of tables, illustrated by maps, in the report. The figures to hand have enabled the Committee to classify them according to group limits for each constituent to facilitate comparison and record variations due to season, weather, type of locality, etc.For each constituent a suitable (low) figure has been selected as the unit, all values below which are grouped as Class A. Class B then includes from 1 to 3 units, Class C from 3 to 5 units, and Class D above 5 units. Thus, in terms of metric tons per square kilometre per month, the units are as follow : For total deposited solids, 5 tons; for insoluble matter-tar, 0.05 ; carbonaceous matter other than tar, 1 ; ash, 2 ; for soluble matter-loss on ignition, 0.75 ; ash, 1.5 ; total solids, 5 ; sulphates, 1 ; chlorine, 0.3 ; ammonia, 0.05.The units have been selected so as to include a few stations in Class A and a few in Class D, leaving the majority of the stations to be included in one or other of the intermediate classes. Certain exceptional conditions may influence the results from particular stations-e.g., the prevalence of tarred roads may increase the tar, and proximity to the sea the chlorine, etc. The dividing line between Class B and Class C represents, in a manner, the average atmosphere of the winter months, a period during which pollution by domestic fires is at a maximum.116 INSTITUTE OF CHEMISTRY The effect of copious rainfall appears to be to increase the precipitation of solid matters in the immediate neighbourhood of the polluting areas, although its effect over the whole country would show an improvement due to the ‘‘ washing” of the atmosphere and diminution of mineral dust. J. F. B.