356 Professors W. B. and R. E. 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. 



To 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, closed at one end, and graduated 

 at this extremity to fiftieths of a cubic inch. Pouring 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 

 to produce as little agitation as possible, and then add mercury 

 until the tube is completely filled. Inverting the instrument in 

 a bowl of mercury and supporting it in an inclined position, we 

 apply 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 air, 

 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 a 

 cubic inch as equivalent to 0047 grain. 



This supplemental process, though seemingly tedious and 

 troublesome, is readily completed in from fifteen to twenty min- 



