fr 
104 Professors W. B. and R. E. Rogers 
gas. It is important, however, to remark, that using-a much ~ 
larger proportion of hydrochloric acid with the water of the 
reservoir, distinct traces of this substance may be detected in the 
issuing gas, and to remove all chance of error, therefore, after each 
new charge of acid, the gas was carefully tested by transmission 
through the solution of nitrate of silver. 
the Hygrometric State of the Gas.—Excepting in the ex- 
that in repeated trials, with gas previously dried and saline solu- 
tions, there occurred an irregular expansion of the gaseous vol- 
ume in the first stage of the action, which did not show itself 
when the undried gas was used. Such an enlargement, due — 4 
evidently to the rise of aqueous vapor into the dry space in the 
first moments of the agitation, being of variable amount accord- 
ing to the solution used, would form a serious obstacle to the ex- 
act measurement of the absorption. 
In the case of the sulphuric acid and other bodies referred to 
as exceptions, this would not take place. On the contrary, the 
esence of aqueous vapor in the gas would here involve other 
errors, due to the absorption of the vapor by the liquid, or to the 
heat disengaged by their reaction. 
The drying of the gas being thus prohibited in a great majority 
of the experiments, it became important to ascertain whether the 
earbonic acid, coming from the gasometer, was saturated with 
vapor, as in this case, from the observed absorption of the moist 
gas, it would be easy to compute the amount of dry gas which 
had actually disappeared. 
For this purpose, the acid solution in the gasometer was allow- 
ed to continue its action until it became entirely neutral. A 
measured volume of the gas was then passed very slow/y through 
along drying tube of chlorid of calcium, previously counter. 
poised. By preliminary trials with an additional smaller tube, 
similarly charged, it was ascertained that scarcely a trace of mois 
ture escaped absorption in the long tube. Before the second weigh- 
ing of the latter, it was freed from carbonic acid by aspiration, 
the smaller tube being attached to prevent the entrance of atmos- 
pheric moisture. In repeated experiments thus performed, the 
