Hygrometry. ^ 
ments, which required inftruments of various fizes, I made 
that cage 1 8 inches high and 2 deep ; but it may be much 
fmaller for common hygrometers. The whole veflel, , except 
that fpace, has been filled, through the openings c, c, with 
quicklime taken, from the kiln, and fuffered only to lofe the 
red heat ; after which the openings were covered with heaps of 
the fame lime, which abforbed the moifture of the air entering 
the veflel while it was cooling, and then the openings were 
fliut with tin plates and putty. The top of the veflel has four 
fquare openings d, d, d, d, correfpondent to the wire cage, for 
the introdudion of the inftruments, which are hung to hooks. 
I ufe a hooked wire for putting in or taking out the inftru- 
ments, to avoid bringing my fingers near the openings. Thefe 
are kept fruit with tin plates and putty : I never open but one 
at a time, which I leave open as little as poflible ; and to pre- 
vent the introdudion of the external air in thofe fhort opera- 
tions, I make them as nearly as poflible at the fame tempera- 
ture, which being 6o° of Fahrenheit may be obtained in 
every feafon. With thefe precautions, and alfo by moift air 
being lighter than dry air, there is fcarcely any moifture intro- 
duced iu the veflel except by the inftruments themfelves, 
5. This application of my method afforded me a very ftrong 
confirmation of the pradical fixity of the point of drynefi pro- 
duced in that manner by lime : for the apparatus was different 
from the former ones ; ift, by the quantity of the lime ; 2d, by 
the lime having been put very hot into the veflel, while, when I 
ufed glafs veflels, I had fuffered it fometimes to cool down to 
6°° ; 3d, by that lime being of the firft calcination, inftead of 
oia lime brought again to white heat ; and all thefe differences 
produced no fenfible effed on the point of drynefs. Since that 
time Mefi. Nairne and Blunt, Mr. Hurter, and Mr. 
Haas, 
