284 Chemical Analysis of the Atmosphere. 
in the Journals of the Société 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.* His researches are. 
great importance to meteorology. Although the method pursued by. 
this: p. hilosopher 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- 
is » 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 den 
scribed ; having first tried the method practised by Thenard and de 
Sues, as well as others, without obtaining results satisfactory t0 
myself. ‘The method by which I at last succeeded is the following. 
A tube of glass three feet long (Fig. 3.)} and of the same cali- 
bre as the hygrometric tube, is filled in the first two thirds of its 
length ab, with hydrate of lime; the rest is disposed so as to serve — 
as a hygrometric tube by putting into.it amianthus moistened with 
sulphuric acid.{ By the increase of weight of this tube, after ® 
measured current of air has passed through, we determine the lide 
portion of carbonic acid it contains. The following details. ee 
dispensable. 
1. The hydrate of lime must be carefully prepared. The imes 
well calcined, is reduced to a hydrate by moistening it with. a few 
vee of water, and after it has completely « crumbled, add a few drops : 
water, so that in stirring it with a spatula it will form 
rs or — It is important to hit the pec: degree of humidity. © 
ee 
bad Via. Mellie Satins. tesonee Vol. XX, p pt” 
i The tube is bent as shown in the figure, in oe sere placed more come 
niently i in the balance. 
r — from the lime, by a few fragments of 
glass or porcelain, actenslae the bend 6. 
