on the Absorption of Carbonic Acid Gas by Liquids. 103" 
phuric acid, require a longer time, but even with the last named 
substance which i is one of the most sluggish in its action, the ab- 
sorption reaches its limit in less than thirty minutes. 
Purity of the Carbonic Acid.—The gas used in our experi- 
ments was supplied by the reaction of dilute ER acid 
and fragments of calc spar, contained in the self-regulating ap- 
paratus figured in the preceding diagram. For sometime, after 
charging the vessel with water and acid, the gas Hyde contains 
a marked proportion of atmospheric air, derived 
originally present in the water, and which is neal. tina a 
as the carbonic acid is absorbed by the liquid. This admixture 
with air was found to continue until the solution became we 
charged with the gas, and this-result, in the ordinary use of the 
apparatus, was very slowly attained. ‘To hasten the saturation, 
and thus bring the materials into a condition to furnish unmixed 
gas, the action of the acid liquid on the carbonate was renewed 
at short intervals, by opening the stop-cock of the reservoir, and 
in this way in a few hours the gas evolved was almost absolutely 
exempt from atmospheric air. 
At the commencement of each set of experiments, a specimen 
of the gas, two cubic inches, was passed into a tube over mercury 
and tested by a moist fragment of caustic potash. When the 
contents of the reservoir were in a proper condition, the residuum 
of unabsorbe gas in this experiment was a mere globule, rarely 
more than ;',th of - inch in diameter, and therefore indicating 
from crinath to to asth of gaseous impurity. 
Thus assured of 1 e almost total absence of atmospheric air in 
the gas supplied under these conditions, our next precaution was 
to determine the degree of purity it retained, when eynny. as 
in our experiments, by simple displacement into the and 
measuring tube. For this purpose a V shaped tube, Sightocn 
inches 
vessel and tube eae for five minutes. The stop-cock of ihe 
tube was then closed, the open end stopped with the finger, and 
the tube detached and inverted over mercury. ‘The contents 
Were now examined in the usual way with caustic potassa. Ina 
number of such trials, made at different stages of our investiga- 
= we found the amount of residual gas to range from about 
resath to ;ss,th of the entire volume employed. In the ab- 
sorption apparatus, the charge of gas is probably less, and certainly 
not more contaminated with atmospheric air than in the trials ae 
mentioned, and can therefore involve no sensible error from this 
source. 
It remains to ascertain how far the CO,, escaping from the 
gasometer, might be mingled with hydrochloric acid. The pres- 
