356 Professors, W. B. and R. FE. Rogers 
vations have proved to us that, even after two protracted aspira- 
tions, the amount of carbonic acid retained by the liquid, is far 
too considerable to be overlooked, and that to effect its complete 
separation, it is necessary to boil the liquid. 
o separate and measure this portion of the carbonic acid, we 
employ a tube of thin glass, about twenty four inches long and 
one fourth of an inch in calibre, closeg at one end, and graduated 
at this extremity to fiftieths of a cubic inch. Ponsing mercury 
into this, until the vacant space above is not much more than suf- 
ficient to contain all the liquid in the bottle, we pour the liquid 
upon the mercury, holding the tube in an inclined position, so as 
* produce as little agitation as possible, and then add mercury 
il the tube is completely filled. Inverting the instrument in 
| of mercury and supporting it in an inclined position, we 
Bly the flame of a spirit lamp to the part containing the acid 
solution. But little carbonic acid is evolved, until near the boil- 
ing point. The bubbles then rapidly ascend and the gas contin- 
ues to be disengaged even after the commencement of ebullition, 
so that to ensure its entire separation, this temperature should be 
maintained for two or three minutes. The tube, placed in an 
erect position, may now be brought to the temperature of the 
apartment by a moist cloth. 
A saturated solution of common salt being poured upon the 
mercury in the bowl, the tube is to be raised a little, so as to per- 
mit this liquid to ascend and take the place of the mercury in the 
tube, after which the instrument is transferred to a deep, narroW 
jar, filled also with the saturated solution, and is depressed to the 
proper level for measuring the volume of the included gas. AS 
this volume always includes a minute quantity of common ait, 
disengaged from the liquid by boiling, the tube must now be 
transferred to a large cistern of water, when by continued agita- 
tion for a minute or two, all the carbonic acid will be absorbed, 
and thus its volume made known by subtraction. These pro- 
cesses being conducted at or near the temperature of the room, 
or the volume being corrected for expansion, should the tempera- 
ture be much higher, the height of the residuary carbonic acid 
is given with sufficient accuracy, by estimating each tenth of @ 
cubic inch as equivalent to 0-047 grain. 
This supplemental process, though seemingly tedious and 
troublesome, is readily completed in from fifteen to twenty mit- 
eee 
bie i 
