large supply of heat energy the flame does not spread and the reaction 

 takes place only in the hottest part of the electric flame. 



Although these methods have only an efficiency of some sixty 

 to seventy per cent, yet where an abundant supply of cheap power 

 is available they seem likely to hold their own, at least for a time. 



It must not be supposed that this is by any means the only 

 method of fixing the nitrogen of the air ; there are several others, some 

 of which seem likely to take an important place in the production of 

 fertilizers and similar nitrogenous compounds. One of the earliest 

 and also the most successful was the formation of what is called 

 cyanamide, a compound of calcium with carbon and nitrogen which 

 easily gives off ammonia. You are all familiar with the carbide 

 which we use for the production of acetylene ; it also is a product of 

 the electric furnace and is produced by heating very strongly a mixture 

 of lime and coal. Now it was found by Frank and Caro that if this 

 carbide were heated in an atmosphere of nitrogen the latter was 

 absorbed, with the formation of calcium cyanamide, a substance 

 which though stable under ordinary conditions is decomposed in the 

 presence of water, with the formation of ammonia. This material 

 has now been on the market for some years and has been extensively 

 used as a fertilizer. It is generally regarded as inferior to nitrate 

 because it may exert a harmful action on the crop if it is used 

 without sufficient care. 



Two methods are employed for obtaining a supply of pure nitrogen 

 for the manufacture of cyanamide. In the first, which is purely 

 chemical, air is passed over heated copper which removes the oxygen, 

 leaving nitrogen, which is collected in holders and then pumped into the 

 furnace containing the heated carbide. The oxide of copper is reduced 

 by means of a current of "producer" or "water" gas, when it will 

 again be ready to absorb oxygen. This method is, I believe, already 

 obsolete. It has given way to a physical method by which the two 

 gases, oxygen and nitrogen, are separated by a process of fractional 

 distillation. This process, which is really very similar to that employed 

 in the production of strong spirit from a weak solution of alcohol, 

 such as is produced by fermentation, is in reality merely a process of 

 rectification. 



The air is first liquefied by great pressure and cold and then 

 rectified in an apparatus very similar in principle to that employed 

 in the manufacture of alcohol. 



Nitrogen boils at 196 C. 77 absolute 

 Oxygen boils ab 183 90 



The final result of the process is that pure nitrogen comes away 

 as gas and liquid oxygen may be continually drawn off from the 



