REGNAULT’S HYGROMETRICAL RESEARCHES. 621 
second with a current which lasted three hours. The weight of 
water was found exactly the same in these two experiments. 
In ordinary experiments the aspirator was emptied in 12 15™ 
to 15 30™. Every five minutes the thermometer placed in the 
case was read off at a distance with a telescope, and the mean 
of the temperatures noted down during the experiment was 
adopted as the temperature of the saturated air. These tem- 
peratures, moreover, varied very little,—one or two-tenths of 
a degree at most. When the vessel ceased to run, a few 
minutes were allowed to elapse for the air of the aspirator to 
take an equilibrium of pressure with the external air, the stop- 
cock 7 was closed, and at the same instant the thermometer T 
of the aspirator and the barometer were noted. The two 
absorbing tubes were then detached and weighed. 
In these experiments I employed indifferently two aspirators, 
which I shall designate 1 and 2. These aspirators were accu- 
rately gauged by weighings. The aspirator 1 contained 58699°8 
grms. of water at the temperature 18°93; it would contain 
58779 grms. of water with the density which the latter possesses 
at the temperature of 4°. The aspirator 2 contained 57457°5 
grms. of water at the temperature 16°62; it would contain 
57513 grms. of water at 4°. 
We shall admit 00000366 for the coefficient of the cubic dila- 
tation of the sheet-iron. The volume of the aspirators at the 
temperature of 0° is therefore— 
For 1. . . . . 58738 cubic centimetres. 
For 2..... 57480 ove coe 
In order to obtain the quantity of water contained in the air 
saturated at 0°, I employed the following arrangement :—A tin 
tube (fig. 3) 0™55 long and 0™:10 in diameter, bears in its axis a 
tube a 6 0™-02 in diameter. This tube is open at its two ends; a 
lateral tubulature cd connects the tube a 4 with the external air. 
The first tube, containing pumice-stone moistened}with sulphuric 
acid, is fitted into this tubulature by means of a cork. The tube 
ab is corked at a. The case is filled with pounded ice; the 
water proceeding from the melting of the ice runs off by the 
stopcock r. 
When the aspirator is in action the external air is drawn 
through the ice, which lowers it to 0°; it penetrates into the 
tube ab by the lower aperture 4, and thence it passes into the 
drying tubes by the tubulature ¢ d. 
