Chemical Analysis of the Atmosphere. 281 
the eudiometric methods show no greater discrepancy than the errors 
which may be regarded as inseparable from experiment. The chan- 
ges h however which we observe in the atmosphere,—the varying phe- 
nomena of meteorology, would naturally lead us to think that these 
proportions must undergo some changes ; 5 and although our experi- 
ments do not justify such a supposition, it is desirable to ascertain with 
certainty the variations, if any do occur, however small they may be. 
The two other substances, which are generally regarded as acci- 
dental constituents of the air, water and carbonic acid, have equally 
engaged the attention of chemists. The estimation of the water con- 
stitutes the special branch of Physics called hygrometry, on which 
subject we have a great number of very valuable researches. ‘The 
valuation of the carbonic acid has been less attended to. We are in- 
debted to Theodore de Saussure for an interesting memoir on this 
subject. 
Although the recent works on these latter points of physics _ 
little to be desired in relation to the exactness of the method em- 
ployed, I think it may be useful to possess various methods, based on 
different principles, and which may on that account serve as checks 
to each other, and ore lead to that exactness which this deli- 
‘eate part ¢ pears to require. It is with this view that 
Thave undertaken a series of experiments for obtaining an easy and 
sure method of determining in a direct mamer the quantity of wa- 
ter and carbonic acid contained ina given volume of atmospheric air. 
AL Determination of the watery vapor eoulamaed : an. the atmosphere. 
OA (Fig.1.) is a cylindrical vessel of glass or metal,—tin for exam- 
eis ——having two openings a and 6, the latter furnished with a stop 
cock. It contains about thirty quarts of water. The upper orifice 
a being connected with a horizontal tube of glass, it is evident that 
‘ethe water which flows through the cock 6 is replaced, in the v es 
by an equal volume of air passing through the tube. By filling 
latter with a hygrometric substance, capable of ‘retaining the watery 
‘vapor which this air contains, we determine by the increased weight 
which the tube thus acquires, the proportion of water contained i in a 
‘Volume of air equal to that of the discharged water. 
~ "To use this very simple apparatus with perfect certainty; severdl 
“Conditions are requisite. 
“1. The vessel A must contain at least thirty quarts in ordet 06% 
‘upon a considerable volume of air. Although in common — 
Vou. XXII.—No. 2: 36 
