VARIATIONS OF THE AMOUNT OF CO, IN THE GROUND-AIR. 



697 



100 c.c. of the solution. The stoppers of the bottles were paraffined, and the Pettenkofer 

 tubes carefully closed by rubber and glass rod stoppers. Three experiments of each were 

 made: — - 





Original Strength 



of Baryta Solution 



in terms of 



the Oxalic Acid 



Solution. 



1. 



2, 



3. 



Pettenkofer Tubes after 1 hour. 











A, 



45-2 c.c. 



45-2 



45-15 



45-2 



B, 



>) 



45-15 



45-2 



45-25 



Glass Stoppered Bottles after 8 hours. 











c, 



)> 



45-2 



45-15 



45-15 



D, 



>> 



45-15 



45-2 



45-15 



These variations from the original titre of the baryta solution are fairly within the 

 limits of error of observation, and cannot be attributed to any action of the glass. 



The oxalic acid solution used for titrating the baryta solution is made by dissolving 

 1"4107 gramme recrystallised and air-dried oxalic acid in 1 litre distilled water. Each 

 c.c. of this solution is equivalent, in combining with barium hydrate, to 0*25 c.c. carbonic 

 acid at 0° C. and 760 m . By using this strength of acid, Pettenkofer pointed out that 

 there is a gain in accuracy and quickness. 100 c.c. of the baryta solution, as we have 

 seen, are used in each experiment. Now, instead of titrating the whole of the solution 

 with an acid, each c.c. of which is equal to 1 c.c. of carbonic acid, we titrate one-quarter 

 of this (25 c.c.) with an acid, each c.c. of which is equal to one-quarter of a c.c. of carbonic 

 acid. In both cases the number of c.c.'s of oxalic acid used is the number of c.c.'s of 

 carbonic acid which 100 c.c. of the baryta solution is equivalent to. Three separate 

 titrations can be made from each experiment without disturbing the precipitated carbonate 

 of barium, giving thus an opportunity of checking the work. Two out of three should be 

 the same. 



Oxalic acid solution decomposes if kept long, and on this account sulphuric acid, 

 diluted to be equivalent to it, is sometimes used instead. In this research oxalic acid 

 solution only was used, and was freshly prepared weekly. The tabulated results at the 

 end of this paper are expressed in c.c.'s per litre at the temperature of 0° C 



The analysis of ground-air shows that it is simply atmospheric air with its oxygen in 

 part replaced by carbonic acid, with the occasional presence of some other gases, e.g., 

 ammonia and carburetted hydrogen. Various observers have found that the sum of the 

 oxygen and carbonic acid in it is nearly equal to the oxygen in atmospheric air. 



Boussingault and Levy state that when the sum of the two gases is in excess of the 



