284 Chemical Analysis of the Atmosphere. 



in the Journals of the Societe de Physique de Geneve, is the result of 

 numerous and extensive researches. His process was an improve- 

 ment on the method of Thenard in 1812, and consisted in causing 

 a large and known volume of air to act on barytic water, in a glass 

 balloon, and to calculate the carbonic acid by the carbonate of ba- 

 rytes thus formed. This process, although founded on a theory per- 

 fectly established, presents many difficulties in the execution, which 

 M. de Saussure has overcome and has described with admirable ex- 

 actness. He found that the atmosphere, in its ordinary state, con- 

 tains between 3.7 and 6.2 of carbonic acid in ten thousand parts of 

 air in volume, and he studied the changes produced by the influence 

 of seasons, hours and various local causes.* Hia researches are of 

 great importance to meteorology. Although the method pursued by 

 this philosopher can scarcely fail to attain the object proposed, I think 

 it would be well to possess a second method, if only by way of com- 

 parison. The method, moreover, of de Saussure requires a train 

 of operations which may easily lead into error in hands less careful 

 . than his own, and which, as he informs us, required nine days for 

 each experiment. 



I have endeavored to employ the hygrometric apparatus above de- . 

 scribed ; having first tried the method practised by Thenard and d« 

 Saussure, as well as others, without obtaining results satisfactory to 

 myself. The method by which T at last succeeded is the following. 



A tube of glass three feet long (Fig. 3.)f and of the same cali- 

 bre as the hygrometric tube, is filled in the first two thirds of its 

 length ab, with hydrate of Hme ; the rest is disposed so as to serve 

 as a hygrometric tube by putting into it amianthus moistened with 

 sulphuric acid. J By the increase of weight of this tube, after a 

 measured current of air has passed through, we determine the pro- 

 portion of carbonic acid it contains. The following details are in- 

 dispensable. 



1. The hydrate of lime must be carefully prepared. The lime, 

 well calcined, is reduced to a hydrate by moistening it with a few 

 drops of water, and after it has completely crumbled, add a few drops 

 more of water, so that in stirring it with a spatula it will form small 

 clots or lumps. It is important to hit the proper degree of humidity. 



* Vid. American Journal of Science, Vol. XX, p. 183. 



t The tube is bent as shown in the figure, in order to be placed more conve- 

 niently in the balance. 



t The moistened amianthus is separated from the lime, by a few fragments of 

 glass or porcelain, occupying the bend b. 



