12 
DR. W. MARCET OR A CHEMICAL IRQUIRY IRTO 
and the temperature of the water is recorded, .corresponding to the temperature of 
the air to be analysed, the barometer is again read off. This, of course, is done after 
removing the weights from the bell-jar, and with the air in the bell-jar exactly under 
atmospheric pressure. Thus 1 litre of saturated air at a given temperature and under 
a known barometric pressure was obtained for analysis. The analysis was made by 
taking up 100 c.c. of the normal barium solution with a pipette and introducing it 
into the bottle, which was next screwed upon the cylindei’ and tightened with gas 
pliers. Then the stop-cock closing the cylinder next to the bottle was opened, and by 
turning the cylinder upside down the alkaline fluid was run into it from the bottle, 
when on shaking, the solution at once turned milky. 
A number of experiments were made to find out how long the agitation of the 
cylinder had to be continued to ensure the complete combination of the carbonic acid. 
The experiments were performed both quaiitatively and quanititatively. The quali¬ 
tative test was made by shaking the air with the alkaline solution for a definite time, 
then aspiring this same air into a second similar cylinder in which a vacuum had been 
made, the displacement being effected over water. Tliis air was tested for carbonic 
acid by shaking it with cleaiqbaryta water. 
After agitating for 10 and 20 minutes the presence of carbonic acid in the second 
cylinder was still obvious, but after 30 minutes none was left, the solution of barium 
remaining perfectly clear after brisk agitation. 
The quantitative experiment was made by determining the amount of carbonic 
acid absorbed by the barium hydrate from 1000 c.c. of the same stock of expired air 
after agitating the cylinder during 20 minutes, 30 minutes, or 40 minutes. The 
followino^ results were obtained :— 
o 
After 20 minutes’agitation.CO^ 4T30 per cent, in air expired. 
,, 30 minutes’ ,,.,, 4194 ,, ,, 
,, 40 minutes’ ,,.,, 4183 ,, „ 
Therefore, after 20 minutes, there still remained a small portion of COg unabsorbed; 
the very slight difference between the results obtained after 30 and 40 minutes is 
within the probable error of the analyses. As half an hour’s agitation was objec¬ 
tionable from the length of time, experiments were made to ascertain whether this 
period could not be shortened by determining the COg in the cylinder under a pressure 
exceeding that of the atmosphere. 
For this purpose a cylinder was used into which a round graduated brass plunger 
was introduced—an instrument I had experimented with for some time while searching 
for a good volumetric method of estimating COg. The plunger moving through a 
close-fitting stuffing box was found to be quite air tight, and by depressing or raising 
it the pressure in the cylinder could be increased or decreased by the volume of the 
plunger introduced or wlthdruv'u. 
