NATURE 



325 



THURSDAY, AUGUST 22, 1872 



AIR AND RAIN '' 



Air and Rain. By R. A. Smith, Ph.D., F.R.S., General 

 Inspector of Alkali \\^Drks. (Longmans, 1872.) 



THIS work contains the germs of a system of chemical 

 climatology. It indicates a plan of testing the 

 purity of the atmosphere of localities with regard to cer- 

 tain constituents of organic origin — the debris of living 

 things — by washing the air, and determining the character 

 and amount of the substances in solution by certain micro- 

 chemical methods. By the systematic repetition of these 

 testings, the possibility is foreshadowed that we may be 

 enabled to classify such atmospheres, and actually to 

 assign to them quantitative sanitary values. It thus points 

 out how we may be able to estimate the difference between 

 the vitiated air of the town and the pure air of the coun- 

 try. Our senses and experience tell us plainly of the 

 existence of such differences ; but chemistry has been 

 hitherto powerless to detect them. " It seemed to many 

 as if the eye had obtained a mysterious power of seeing 

 what was scarcely capable of being proved to be within 

 the domain of substance, and the smell had a power of 

 observing what was more an influence than a positive 

 thing." Cavendish, nearly a century ago, asserted that 

 chemical experiments could not distinguish the air of 

 London from the air of the country ; and in spite of the 

 labours of Bunsen and Regnault, Frankland and William- 

 son, which have rendered gasometry more susceptible of 

 refinement and accuracy than any other branch of chemi- 

 cal analysis, this assertion seems as true of to-day as it 

 was of the time when uttered. Hitherto chemists, in 

 judging of the quality of the air of any locality, have been 

 obliged to content themselves with determining the pro- 

 portion of oxygen and carbonic acid which it contains, in 

 conformity with the practice of their ancestors of a cen- 

 tury back. Gradually, however, they have been forced to 

 thS conclusion that such determinations have very little 

 positive value in enabling them to assign a value to the 

 sanitary condition of an atmosphere — that oxygen was no 

 panacea, nor carbonic acid as deadly as strychnine ; and 

 thus we have been thrown back upon our unaided senses 

 to distinguish between the good and the evil. Supposing 

 that some Martin Chuzzlewit, going out to another Eden, 

 required information respecting the sanitary condition of 

 the settlement, the chemist could tell him something con- 

 cerning the water he might have to drink, but he would 

 be utterly unable to enlighten him respecting the air he 

 would be compelled to breathe. Some such considera- 

 tions prompted the inquiries which have resulted in this 

 book. Dalton's assertion that he could not distinguish 

 the air of Manchester from that of Helvellyn, or generally 

 the air which depresses from that which cheers and in- 

 vigorates, seems to have forcibly impressed the author. 

 For upwards of forty years he has laboured to remove the 

 stigma on chemical analysis, and in this volume he con- 

 centrates his thoughts and experimental results. " It was 

 with the desire," he says, " of clearing the mystery of air 

 to some extent that I have devoted so much of my time 

 to the subject ; and now I feel that, whilst I have suc- 



VOL. VI. 



ceeded in doing much of that which I intended to do, I 

 have not got beyond the limits which earlier observers 

 attained by the mere fineness of unaided sense, and by 

 sound reasoning without experiment. Still I hope I shall 

 be found to have put their suspicions into plainer lan- 

 guage, proved that which they only imagined, and given 

 in detail that which they only in a general, and, we may 

 add, in a vague manner, had attained." 



Dr. Smith first sets out by defining the composition of 

 a normal atmosphere, as deduced from the many analyses 

 which have been published, and from numerous supple- 

 mentary determinations of his own made on air collected 

 in various parts of Great Britain and on the Continent. 

 In the outset he insistson the value of minuteness in read- 

 ing the figures ; differences which in the eyes of most 

 chemists are of little value, are to him full of meaning. 

 Every deviation from the standard of purity is to be 

 rigidly criticised. Thus, the difference between 20-980 

 and 20999 in the percentage amount of oxygen means a 

 difference of 193 parts in a million. If this consisted of 

 organic matter, or the gases of putrefaction, it might 

 become of the gravest consequence. Certainly igo parts 

 of putrefying matter in 1,000,000 parts of water— equal to 

 •3'3 grains per gallon— would be considered as an enor- 

 mous quantity. But, comparatively speaking, we drink 

 only a small quantity of water, and the whole 13 grains 

 would not be swallowed in a single day ; whereas we draw 

 through our lungs nearly a couple of thousand gallons of 

 air daily. But, indeed, differences much greater than this 

 are found to exist, Thus, the air of a theatre sometimes 

 contains as little as 207 per cent, of oxygen, and even 

 this is by no means an exceptionally small quantity for 

 such a place ; and yet this amounts to a deviation of 

 3,000 parts in a million from the standard of purity. 



In speaking of the proportion of carbonic acid in the 

 air, the author bases certain considerations (p. 11) upon 

 the assumption that this gas is washed out by falling rain. 

 But is this supposition exactly confirmed by experiment ? 

 Saussure, it is true, thought that he could detect a 

 difference in the amount of carbonic acid between the air 

 over the Lake of Geneva and that over the land ; but such 

 differences have not been found by other experimenters. 

 Sea air contains about three volumes of the gas in 10,000 

 volumes ; whilst the air of the land contains only four 

 volumes. But this difference is due more to the influence 

 of the land than to any absorptive action exerted by the 

 sea. Indeed, from a consideration of the laws of gaseous 

 absorption, it can be shown that the pressure exerted by 

 the relatively small quantity of carbonic acid present in 

 the air is unable to bring about any perceptible variation 

 in its amount over sea and land. 



Having fixed on his standard of purity. Dr. Smith pro- 

 ceeds to examine vitiated air and to trace its effects on 

 breathing. For this purpose he used an air-tight chamber 

 in which one or more persons could be seated ; and from 

 time to time he collected and analysed samples of the 

 enclosed air, and compared the analytical numbers with 

 the sensations experienced and noted at the moment of 

 collection. The details of these experiments are of great 

 interest, and merit careful study. That they were not un- 

 attended with danger is evident from the experience of a 

 young lady " who was extremely fond of pure air," but 

 who in the cause of science " was anxious to be in the 



