REGNAULT’S HYGROMETRICAL RESEARCHES. 617 
circumstances of temperature and pressure, 
I have only made a single series of experiments by this method, 
and an accident prevented my obtaining good results. I pur- 
pose shortly to resume these determinations. 
The same apparatus may serve to determine the density of 
aqueous vapour in the air taken under different pressures: in 
this case an ordinary manometer is substituted for the barome- 
trical manometer. But the determinations unfortunately in 
this case no longer present the same precision as im vacuo, and 
this for reasons which I have stated above (page 608), when our 
attention was directed to the determination of the tensions of 
aqueous vapour in the air. 
Let us now direct our attention to the determination of the 
density of aqueous vapour in the uir in a state of saturation. 
We have seen above that this question has been treated of by 
M. Schmedding, who found that the density of the vapour in- 
creased in this case rapidly with the temperature. 
I determined the density of aqueous vapour in a state of sa- 
turation in the air, by weighing the quantity of humidity which 
a known volume of saturated air contains at different tempera- 
tures. For this purpose I employed the process of M. Brunner, 
which consists in filling a vessel of known capacity with water, 
making the upper part of this vessel communicate with tubes 
containing drying substances and which have been exactly 
weighed, and causing the water of the vessel to run off in a re- 
gular manner by an inferior orifice; the water which runs off 
below is replaced, in the upper part, by an equal volume of air. 
The aspirated air is completely deprived of its humidity in 
passing through the tubes. When the aspirator is emptied of 
water, the tubes are weighed; their increase in weight repre- 
sents the weight of the water which existed in a volume of air 
equal to the capacity of the aspirator. 
A similar process was employed by M. Schmedding; but I 
found that, to obtain accurate results, certain precautions must 
be taken. 
The aspirator which I have used is formed of a cylindrical 
vessel of galvanized sheet-iron, terminated by two conical ends. 
The upper end has two tubulatures: the central one a, in which 
