24 



with any graduation mark. Suppose the following observations 

 to he made : 



Height of mercury in C - 250 mm. 



Corresponding volume of gas as perl 109 



calibration table -J 1 



Height of mercury in A - 130'4 mm. 



Temperature of water in H - 16'4 C. 



Height of barometer - - 763 '1 mm. 



From these data the pressure upon the gas is calculated as 

 follows : 



Height of barometer - - 763*1 mm. 



Deduct height of mercury col."] 

 in A from height in C, viz., Ill9 f 6 

 250130-4 

 Plus tension of aqueous vapour"] 



(the interior of C being > 13' 9 



moist) at 16'4 C. - -J 133'5 



Pressure on dry gas - 629'6 



Hence we have 19'2 c.c. of dry gas at 16'4 C. and 629-6 mm. 

 pressure. 



Absorption of Carbon Dioxide. This is effected by pass- 

 ing up into the jar I, by means of a small pipette, two or 

 three drops of a concentrated solution of caustic potash. The 

 gas is driven from the measuring tube C into contact with the 

 potash solution by raising the mercury reservoir and opening 

 the stopcocks. A few minutes' exposure secures the absorption 

 of the carbon dioxide, and the residual gas, a mixture of 

 oxygen and nitrogen, is drawn back into C and measured as 

 before. 



Absorption of Oxygen. A few drops of a concentrated solution 

 of pyrogallic acid are added to the solution of caustic potash in 

 the jar I, and the gas driven from C as before. The alkaline 

 potassic pyrogallate immediately absorbs oxygen, becoming of a 

 deep blood-red colour. By careful manipulation the jar I may 

 be slightly agitated, so as to promote the absorption, which 

 is known to be complete when the dark- coloured liquid thus 

 thrown upon the sides of the glass runs off again without leaving 

 a dark blood-red stain. 



The remaining operation is to determine in C the volume of 

 the residual nitrogen, and the analysis is finished. 



Three uncorrected gaseous volumes are thus obtained, viz. : 

 A= volume of three mixed gases ; 

 B= volume of mixed oxygen and nitrogen ; 

 C = volume of nitrogen. 



By the formula given below these volumes may be reduced to 

 C. and 760 mm. pressure, and then from the corrected 

 volumes A', B' ; and C', so obtained, the quantity of each gas 

 in the mixture may be deduced. 



