1877.] Dr. R. A. Smith on the Examination of Air. 



513 



although my rmraerous engagements may well form a kind of apology. 

 My present object is partly to draw attention to the fact of my proposal 

 and not to let it be forgotten, and it is also combined with another object, 

 namely, to speak of methods of study or experiments which have been tried. 



In obtaining specimens of any soluble or insoluble body from the 

 atmosphere, I have washed the air with pure water — that is, I have shaken 

 the water in a vessel of the air to be examined. 



The other method, chiefly, and I may almost say universally, used, 

 except by me, has been to pass the air through water. 



It is of great importance to obtain the characteristics of each method. 

 It is now many years since I passed air through water for three months 

 and obtained so little of a result, that I gave up the matter for some 

 time in despair. I passed air which I knew to contain acid and salts 

 through water ; but I obtained scarcely any of either, and I afterwards 

 found both in the tubes through which the air passed before entering 

 the water. This little incident made an era in all my inquiries. I tried 

 minutely pointed tubes, but did not succeed, and for the same reason, or 

 rather for that and an additional reason, viz. the minuteness detained 

 the air longer in the tubes, and the result was worse. 



A considerable number of small holes pierced in a bulb at the end of 

 a glass tube having been recommended, I obtained, by the kindness of 

 Mr. Dixon, of Glasgow, a few which he had got made in a beautiful and 

 ingenious manner. I knew from my previous results that the success 

 would be imperfect ; but I thought it well to try any new method and to 

 overlook all my work, quite willing to find that I had been doing in a 

 laborious and imperfect manner that which could have been done with 

 ease and rapidity. I did not find that Kature had altered her habits 

 since my previous and numerous trials ; but I found that the small holes 

 prevented still more the exit of particles which floated in numbers in 

 the bulbs. 



The tubes retain not merely visible particles but those invisible, although 

 by accumulation some of the latter also become visible, and give a turbid 

 character to the liquid or a dimness, according to the amount of moisture 

 and the hygrometric character of the substances. 



The washing of the air is laborious, because the water must be shaken 

 up violently within the bottle. In order to refill the bottle with air, an 

 air-pump must be used until the required point is obtained on the mercury 

 gauge, this being found to indicate a known amount of air, which is now 

 allowed to enter so as to be washed exactly as the former quantity. To 

 obtain the hydrochloric and sulphuric acid only in the air of Manchester, 

 this operation must be repeated fifty times ; with some pure air as much 

 as 200 bottles have been used. It is not to be supposed that in such 

 laborious measurements the fullest accuracy is attained ; but, as I have 

 said elsewhere, at least good comparative results are found. I know 

 well the great importance of obtaining a ready method, and I am not 



