SCIENCE 



NEW YORK. OCTOBER 13. 1893. 



THE AIE OF LARGE TOWNS. 



BY G. H. BAILEY, D.SC, PH.D., THE OWENS COLLEGE, MANCHESTER, 

 ENGLAND. 



During the past three year8|a series of investigations have 

 been in progress in England with a view to ascertain the 

 composition of the air in populous districts under vary- 

 ing meteorological conditions. The Royal Society, the 

 Royal Horticultural Society and the Manchester Field 

 Naturalists have assisted the work by grants towards the 

 cost of the requisite apparatus, and your readers may be 

 interested in the resiilts which have been obtained, al- 

 though, of course, it is only possible to give a very brief 

 summary of them. General experience has shown that 

 evergreens cannot be grown in the heart of our larger 

 cities and even the more hardy deciduous trees make lit- 

 tle progress and sooner " or later succumb. The sulphur- 

 ous and other noxious vapors and the deposits of soot, 

 hydrocarbons, etc., which form on the leaves are the chief 

 agents in the destruction of plant-life. 



Moreover, during periods of fog, when the air is sur- 

 charged with such impurities, the amount of sickness and 

 the death-rate increase very considerably, especially in 

 regard to diseases of the respiratory organs. The death- 

 rate indeed from such diseases after foggy weather fre- 

 quently increases to three-fold its normal value and is 

 always exceptionally high in the densely populated dis- 

 tricts. 



Seeing that very few analyses of town air have been 

 made embracing impurities such as sulphur in its various 

 combinations and organic matter, attention was particu- 

 larly devoted to these. And, indeed, setting aside the 

 import of such forms of pollution from a sanitary point 

 of view, the variations in sulphur compounds and organic 

 matter may well be taken as means of differentiating be- 

 tween town and country air and of comparing together 

 the condition of the atmosphere in different districts of a 

 town. The method of procedure was to establish in Lon- 

 don, Liverpool and Manchester and their suburbs a num- 

 ber of observing stations where determinations were peri- 

 odically made of the composition of the air, of the charac- 

 ter of the rain and snow and of the intensity of light. 

 Comparative measurements were also at times made in 

 country districts and in parts (such as Switzerland) where 

 the air is of a great degree of purity. 



From a very large number of observations I may sum- 

 marize as follows : 



(1) Country air and the air of the less populous parts 

 of towns under the most favorable conditions show an 

 amount of sulphur existing as sulphurous and sulphuric 

 acid, etc., equivalent to not more than one volume of sul- 

 phurous acid per ten million volumes of aii\ 



In populous districts this was found to rise to ten vol- 

 umes as a general average in the Winter months and about 

 five in the Summer. During dense fog such as occurs 

 with tolerable frequency during the Winter, the amount 

 recorded has been from thirty to fifty volumes. Whilst, 

 therefore (as already found by previous observers), the 

 carbonic acid gas during foggy weather is only about 

 double that ordinarily occurring, the sulj)hur compounds 

 accumulate so as to reach from twenty to fift3r-fold their 

 normal amount. 



(2) Licrease of a similar order was found to take place 



in the suspended organic matter of the air, and not only 

 so, but the increase in amount, especially in closely 

 crowded districts, was associated with a greater virulence. 

 A critical examination was also made of the nature of 

 the deposits carried down during foggy weather, and as an 

 instance I may give the composition of sample collected 

 at Chelsea (London). 



Carbon, - - - 39 per cent. 



Hydrocarbons, - - - 12.3 " 



Organic bases (pyradines), - 2.0 ' 



Sulphuric acid, - - - 4.3 " 



Hydrochloric acid, - - 1.4 " 



Ammonia, . - _ 1.4 " 



Metallic iron and magnetic oxide, 2.6 " 

 Other mineral matter, chiefly silica, " 



and ferric oxide, - 31.2 " 



Water _ _ . not determined. 



(3) With regard to the prevalence of black fogs we are 

 fortunate in having records (kept by Dalton) which indi- 

 cate that in the earlier part of this century, Manchester, 

 with a population at that time of about 120,000, had on 

 an average about four or five dense fogs during the win- 

 ter, whilst at the present day (with a population of half a 

 million) we have dense fog lasting the whole day on 

 twenty days or more and fogs of less density are experi- 

 enced on forty or fifty days. 



The number and nature of the fogs vary, of course, ac- 

 cording to the season, but this may be taken as a general 

 expression of the state of things now. 



(4) Measurements of the extent to which the actinic 

 rays are cut off by smoke and haze show that the central 

 areas of our large towns suffer a very large diminu- 

 tion, amounting to a loss of from thirty-five to fifty 

 per cent aa compared with the suburbs. That 

 these suburbs are themselves by no means removed 

 from the influence of smoke is evidenced by the fact that 

 under like conditions the values obtained at Torquay and 

 at Grindelwald in Switzerland were three-fold and six-fold, 

 respectively, of those given for the suburbs of London 

 and Manchester. In foggy weather ninety-five per cent 

 or more of the actinic rays are cut off. 



(5) Determinations of the number of bacteria and 

 moulds occurring in the air show thatagain in this respect, 

 also, the contrast between town and country air is very 

 marked indeed, and that in all such determinations due 

 allowance must be made for the meteorological conditions 

 prevailing at the time of experiment. The effect of im- 

 purities, such as sulphurous acid on micro-organisms, is 

 also being studied. 



Though in the previous paragraphs it has only been pos- 

 sible to deal in the most general manner with the results 

 obtained, the remarks will, I hope, be sufficient to give 

 point to a request that I should like to lay before your 



Smoke arising from the combustion of coal is undoubt- 

 edly the primary cause of the pollution of town air either 

 directly or indirectly; directly in its contribution of 

 sooty matters, hydrocarbons, sulphurous acid, etc., and 

 indirectly in promoting a condition of the atmosphere in 

 which free diffusion is very much interfered with and lead- 

 ing therefore to the accumulation of sewer gases and 

 emanations from decaying refuse in the lower stratum of 

 air. The substitution of gaseous fuel, though it may not get 

 rid of fogs altogether, will doubtless mitigate in a very 

 large measure their noxious character and ia the era 



