HYDROGEN GAS 



39 



hydrogen apparatus, in such a way that the purified gas is led 

 into the top of the flask while the air is driven out from the 

 bottom. When every trace of air has been expelled, and it is 

 completely filled with the hydrogen, detach the flask, stopper 

 and weigh it. Now, by means of an aspirator, draw air, dried 

 by slowly passing through the calcium chloride tube, into the 

 flask the reverse way, until all the hydrogen has been driven 

 out ; detach, stopper, and weigh again. Next find the capacity 

 of the flask by filling the flask and tubes with water and 

 measuring the water. At 15° C, the temperature at which both 

 the air and hydrogen should be, and when the barometer stands 

 at 30 inches, 1000 c.c. of dry air weighs 1.226 grams. From 

 this calculate the weight of air in the flask, and subtract it 

 from the weight of the flask filled with air, in order to deter- 

 mine the weight of the flask. The weight of hydrogen can 

 now be determined by subtracting the weight of the flask from 

 the weight of the flask and hydrogen. The weights of equal 

 volumes of air and hydrogen being now found, calculate the 

 relative density of air, taking hydrogen as i, and that of hydro- 

 gen, taking air as i. Repeat the determination until concor- 

 dant results are obtained. 



In the foregoing experiment great care must be taken completely to fill 

 the flask with the gas. Until stoppered the flask must on no account be 

 touched with the hands, as this would warm and expand the gas. The 

 ollowing example will serve to illustrate the method of working : — 

 Capacity of the flask = 1000 c.c. 



icxx) c.c. of dry air at 15° C. and 760 m.m. pressure weighs 1.226 grams. 

 Weight of flask and air = 101.226 grams. 



Weight of air = 1.226 ,, 



Weight of flask = 100.000 „ 



Weight of flask of hydrogen = 100.085 grams. 

 Weight of flask = 100.000 ,, 



Weight of hydrogen = 0.085 ,, 

 Hence if air = i, the relative density of hydrogen = .069, and if 



