8 



Chapter I 



manometer. The measurement consists in reading the difference in 

 the level of the fluid surface on each side ; the problem is to turn 

 this difference of level read in mm. of clove oil into a measurement of 

 quantity in cubic centimetres of oxygen which has been liberated. 



FIG. 1. Form of differential apparatus used in Peters' and Burn's researches. 



It may be shown mathematically that if x be the difference in 

 level of the fluid surfaces, V the volume of air in each bottle, a the 

 sectional area of the tubing, p the barometric pressure in mm. of 

 clove oil, and q the quantity of oxygen liberated, all the quantities 

 being expressed in mm., 



'- 

 P 



Now the quantities V, p and a are measurable, and V and a 

 may be measured once for all. It was by this method that Peters 

 calculated the relation of q to x in his experiment. There is no 



