Gravimetric Determination of Carbon Dioxide. 103 
to protect the barium hydroxide from the action of the carbon 
dioxide of the air. By manipulating the balloon and the stop- 
cock (to which a little funnel may be attached by a piece of 
rubber tubing for convenience in introducing wash-water) the 
cylinder may be emptied and washed out with hot boiled 
water, though, of course, a very considerable portion of the 
precipitate remains adhering to the walls of the absorbtion 
apparatus. 
We prefer to prepare the filter for use with the suction 
pump, but in the early stages of filtration and washing very 
little suction should be applied. When the barium hydroxide 
has been nearly washed out of the precipitate, the xylene is dis- 
solved in a little hot alcohol, the suction is applied and the 
washing is completed with hot water. The emulsion of xylene 
and water found in the filtrate is readily cleared up by alcohol. 
Finally, the barium carbonate in the absorbtion apparatus and 
upon the filter is dissolved in hydrochloric acid and precipi- 
tated in hot solution by sulphuric acid, the resulting barium 
sulphate is filtered, washed and ignited upon asbestos in a per- 
forated crucible, and from its weight the carbon dioxide which 
originally precipitated the barium, now in the form of the sul- 
phate, is calculated. The results of a series of determinations 
made in this manner are recorded in the following table: 
[Ba 187-43, 5 = 32:06, O = 16, © = 12,] 
CO . 
CaCO; BaSO,4 Sail CO, Error in 
taken. found. present. caleulated. CO, 
erm. orm. orm, orm, erm, 
0°0500 0°1180 0°0220 0°0222 0°0002 + 
0°0500 0°1183 0°0220 0°0223 0°0003 + 
0°1000 0°2329 0°0440 0°0439 0°0001— 
1'1000 0°2347 0°0440 0°0442 0°0002 + 
0°2000 0°4660 0°0880 0:0878 0°0002— 
0°2000 0°4653 0°0880 0:0876 0°0004 — 
0°5000 1°1650 0°2200 0°2196 0°0004— 
0°5000 1°1657 0°2200 0:2197 0°0003 — 
1°0000 2°3323 0°4400 0°4396 0:0004 — 
10000 2°3309 0°4400 0°4394 0:0006 — 
Various modifications of method and manipulation were put 
to the test of experiment, but the process which we have 
described has proved on the whole the most satisfactory. It is 
fairly rapid and accurate. 
