OXYGEN AND NITROGEN 251 



and oxygen, delivered from their respective cylinders meet, and 

 when ignited produce a pointed flame of which the temperature 

 is considerably higher than that of a mixture of oxygen and 

 hydrogen. A flame of this kind can be used for welding together 

 iron surfaces of all kinds. 



The use of the blowpipe, however, is still more wonderful in 

 the feats which it is now capable of performing in the direction 

 of cutting thick sheets of metal. In this case the oxy acetylene 

 flame is produced at the mouth of the blowpipe, and through 

 the middle of this a pointed oxygen flame is directed on the 

 surface of the iron or steel to be cut. The following quotation 

 from Thorpe's Dictionary will serve as a sufficient illustration 

 of the capacity of the method. 



" A plate 12 inches thick of nickel chrome steel armour plate 

 was cut through at the rate of 1 foot in 4| minutes with a con- 

 sumption of 50 feet of oxygen per foot run." 



With such an instrument at hand the older shearing, sawing, 

 and boring methods of the engineering workshop are likely soon 

 to disappear. 



The illustrations Figs. 67, 68 convey an idea of the apparatus 

 required for the production of liquid air and the separation of 

 the oxygen and nitrogen from it. The principles made use of in 

 the cooling of a gas below its critical point, and the system of 

 intensive or cumulative cooling have already been explained 

 sufficiently in the chapter on apparatus (p. 85). It is therefore 

 unnecessary to do more than indicate with the aid of the plan 

 the relative positions of the several parts of the machinery. The 

 description which follows is taken from an article in Engineering, 

 vol. 87 (1909). The plant at Odda on the Sondre Fiord, Norway, 

 for the production of the nitrogen required in the manufacture 

 of cyanamide, was " constructed by the Linde Eismaschinen 

 Gesellschaft, Munich ; the English patents are held by the 

 British Oxygen Company Limited. The process is the invention 

 of Professor Linde. It is based on the fact that at atmospheric 

 pressure nitrogen boils at -196 deg. Cent. ; liquid air boiling at 

 -194 deg. Cent. ; and liquid oxygen at -183 deg. Cent. 



" By using the well-known rectification process followed in 

 the manufacture of alcohol, the nitrogen can be completely 

 separated from the oxygen. The Linde Company guarantees 

 that the nitrogen does not contain more than 0*4 per cent of 

 oxygen, a percentage which has neither an unfavourable influence 



