758 The Outline ot Science 



and other processes. Nitrogen, as we have seen, is obtained from 

 the air on a great scale for the manufacture of fertilisers, the out- 

 put of which, is enormous. Argon and neon also are trapped from 

 the air and are used in incandescent electric lamps. 



We cannot leave the subject of "fertilisers" without saying 

 a little 'about cyanamid. When a strong electric current is passed 

 through a mixture of lime and coke, the metal calcium joins to 

 part of the carbon, yielding calcium carbide (CaCs), the stuff 

 which along with water produces acetylene gas. Now if a stream 

 of nitrogen be passed over hot calcium carbide it is captured and 

 forms calcium cyanamid ( CaCN2 ) , a stony material sold as a 

 fertiliser ("lime nitrogen"). But if the calcium cyanamid be 

 treated with superheated steam, it yields ammonia, and from 

 ammonia can be produced nitric acid, and from that fertilisers, 

 which mean more bread. 



It is useless to pretend, however, that this is more than one 

 side of the story. For whether it be primitive gunpowder made 

 by grinding up saltpetre, charcoal, and sulphur into a black pow- 

 der, -or nitroglycerine, or gun-cotton, or these two combined, or 

 TNT, all the explosives of war depend upon the readiness of 

 "the nitro group" (NOz) to break up. For nitrogen does not 

 readily combine with other elements, and when it does so it is 

 very prone to break off the connection on even slight provocation. 



The Potash Supply 



A typical plant food is saltpetre or potassium nitrate. The 

 nitrate part can now be snatched from the air instead of being 

 dug from the guano-beds of Chile. But what of the potash part? 

 "A ton of wheat," Dr. Slosson says, "takes away from the soil 

 about 47 pounds of nitrogen, 18 pounds of phosphoric acid, and 

 12 pounds of potash." If the farmer is to go on, he must replace 

 not only the nitrogen but the phosphorus and the potash. 

 The world consumption of potash for agricultural purposes is 

 enormous. 



