44 AtiRICULTURAL CHEMISTRF. 



Heavy carburetted hydrogen (C^H') is the gas used 



for lighting. It contains, as shown by its symbol, 

 just twice as much carbon as the other, in conse- 

 quence of which it gives a much stronger light. 

 Heavy carburetted hydrogen may be obtained from 

 almost any substance that contains carbon and hydro- 

 gen, as coal, oil, bark of trees, meats of nuts, &c., by 

 heating it, with exclusion of air. If you put a walnut 

 meat into the bowl of a tobacco pipe, cover it over 

 with clay, and then thrust it into the fire, with the 

 stem projecting "upwards, this gas will soon issue from 

 the stem. If you light it with a candle, you will 

 have a good sample of a gas-light in a small way. 



65. Ammonia (NH") is composed of one atom of 

 nitrogen, 14, to 3 of hydrogen, 1 each, making 17. 

 Consequently 17 lbs. of ammonia contain 14 lbs. of 

 nitrogen and 3 of hydrogen. The peculiar odor of 

 this compound may be recognized in the hartshorn 

 of the shops, when used with quick -lime in the pre- 

 paration of smelling bottles. It is generated where- 

 ever animal matter is undergoing decomposition ; and 

 if left to its own course it quickly combines with car- 

 bonic acid, forming a volatile carbonate of ammonia, 

 and passes off into the air, to be blown about by the 

 winds, and at length to be intercepted and brought 

 back to the earth in the falling rains. In this way it 

 is made to contribute as much to the growth of the 

 useless as of the useful plants ; for the rain, charged 

 with this ammonia, falls as much on the wild moun- 

 tain as on the cultivated plain. There are various 

 easy and cheap modes of preventing its escape, which 



