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374 Bibliography. 
mention. ‘Two air-pumps fixed toa table afforded the pressure, the first 
pump had a piston of one inch diameter, and the second a piston only 
half an inch in diameter, and these were so associated that the first 
pump forced the gas into and through the valves of the second, and then 
the second could be employed to throw forward this gas, already con- 
densed to ten, fifteen, or twenty atmospheres, into its final recipient at 
a much higher pressure. 
The gases on their way from the gas- sholdets to the pump were made 
to pass through a coil of thin glass tube contained in a refrigerator of 
ice and salt, and consequently at the temperature of 0° Fahr., by 
which means any water they contained was effectually condensed. The 
conducting tubes were of green bottle glass, from } to } inch in diam- 
eter, and from 4; to 34 inch in thickness, they were connected by caps, 
and screws, and cocks, with the pumps, and great care was taken that all 
parts of the apparatus should be perfectly tight. These tubes frequently 
sustained the pressures of fifty atmospheres in practice, and to prove their 
strength a hydrostatic pressure of one hundred and eighteen atmos- 
pheres was applied to one having an external diameter of 0-225 of an 
inch and 0:03 in thickness, without any fracture or any leak in the caps 
and cement; a tube having the thickness of 0°01'75 of an inch and an 
external diameter of 0°24 of an inch, burst with a pressure of sixty 
seven atmospheres of fifteen pounds each to the square inch. One such 
as he formerly employed for generating gases under pressure, having 
an external diameter of 0°6 of an inch and a thickness of 0-035 of an 
inch, burst at twenty five atmospheres. The pressure gauge was.as on 
former occasions a small tube of glass closed at one end, and having a 
cylinder of mercury moving init. The graduation was marked on the 
gauge in black varnish and also in Indian ink; the latter stood, but the 
former was dissolved in some of the gases. 
The cold bath in which the condensing tubes were immersed was 
formed of THrLoriEr’s mixture of solid carbonic acid and ether, contained 
in a porcelain capsule of four cubic inches or more, fitted into a similar 
dish somewhat larger with three or four folds of dry flannel intervening ; 
this bath continued from twenty to thirty minutes, retaining solid car- 
bonic acid the whole time, and gave indication by an alcohol thermom- 
eter made for the purpose, of the very low temperature of — 106° below 
0° Fahr.; by placing the bath under an air-pump the temperature fell so 
low, on working the pump, as — 166° below 0°,* or 60° below the tempe- 
* Commencing with the temperature of —106°, as the exhaustion proceeded the 
temperature fell 64° in the first ten inches of the barometer’s rise, 83° in the next 
ten, (or from ten to twenty inches of the barometer,) 4° in the next ten inches, 6° 
from twenty two to twenty four inches, 8° from twenty six to twenty seven inches, 
7° in the next inch, 4° in the next, and 6° from 28° to 283°, when the mercury 
became stationary. 
