354 Liquefaction and Solidification of Carbonic Acid. 
As below 32°, or at reduced pressures, the augmentation of 
temperature is productive of much less expansive influence, we 
may infer that under the weight of a few. atmospheres, as when 
near to its freezing point, liquid carbonic acid is. scarcely more 
dilateable by heat than water. Between —4° and +329, its 
expansion is 0.053 while that of air is 0.069. These facts suggest 
the inquiry how far water at very high temperature and ‘pressure 
may be obedient to the same expansive influence, and thus by 
% 
suddenly filling the whole ay ein of boiler, sometimes cause €X~ 
plosions. 
~The pressure of carbonic acid gas, when slhsata over its liquid; 
is given by Thilorier at 32° and 86°, as 36 and 73 atmospheres 
respectively. ar 2 means of the gauge S, M, R,—I found the 
— as follo ows es 
320 ees 36 tenis dake 
ee age SL a 
NN ee ee ee 
86° - - - 72 do. 
The principle of the gauge renders it capable of registering the 
pressure. with great accuracy ;—for as one tube, M, begins to mark 
the pressure from the commencement of an experiment, and the 
mercury in the-other, R, does not reach a visible point until the 
first has shown ‘a pressure of several atmospheres, the second tube 
is equivalent in effect to one of several times its length. The 
first determines the amount of pressure, at which the mercury 
reaches the initial point on the 2nd, and the 2nd, subsequently, 
exhibits the multiplicators of that sind quality. Thus, if when 
the mercury is at five atmospheres in M, it is at the unit mark 
in R, the value of that unit will be five, and the numbers repre- 
sentative of the pressure on R, must be multiplied by five; or R 
is equal in effect to a tube five timesits length. By these means 
very short tubes may be used to determine very high~ pressures. 
Inequalities in temperature, irregularities in the cement, an 
other causes; may vary the capacity of the socket T, W, but as 
M always signifies the unit for R, in each case, no error can arise 
from these causes. There must, of course, be a correction for 
the weight of the mercurial column in R, which is to be added 
to the product. Care must -be taken to kegp the temperature of 
the vessel which holds the liquid below that of the gauge and. 
tubes, otherwise the liquid will be formed by condensation in 
