SPECIFIC GRAVITY OF HYDROGEN GAS. 69 



necessary to ensure success. Unless the gas be 

 extricated very slowly, the muriate of lime does 

 not dry it sufficiently indeed, I was never able 

 to free it completely from moisture ; but a very 

 simple calculation gave me the weight of the 

 vapour which still adhered to it. The tempera- 

 ture of the liquid should be kept as low as possi- 

 ble, not merely to moderate the fermentation, 

 but to avoid the risk of sulphuric acid escaping 

 along with the gas. When the flask was left in the 

 air, the temperature continued to rise for more 

 than an hour after the experiment began. In 

 one experiment it rose from 50 to 87, in another, 

 from 48 to 81 : the greater the quantity of zinc 

 dissolved, the more accurate (caeteris paribus) was 

 the experiment ; but the quantity was unluckily 

 very much limited by the small size of the 

 flask. 



It will be sufficient if I relate one experiment, 

 during which, all the precautions that I could 

 think of were taken ; and which, I have reason to 

 believe, was very nearly accurate. 



The quantity of zinc dissolved was 143 grains 

 the effervescence continued for 24 hours the 

 temperature never rose higher than 49 the 

 barometer stood at 3O1 inches, and the thermo- 

 meter at 49 the loss of weight was 4*3 grains. 



It will be, perhaps, more perspicuous, if we 

 suppose that 100 grains of zinc only were dis- 

 solved. On that supposition, the loss of weight 



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