TEST FOR NITROGENOUS SUBSTANCES. 185 



powdered soda-lime; the smell of ammonia (mixed with other 

 matters of a tarry nature) will soon become perceptible, and on 

 putting a red litmus paper in the fumes issuing from the mouth 

 of the test-tube it will be rendered blue. 



The production of ammonia in this way is employed as a test 

 to see whether substances are " nitrogenous " or not ; i.e., whether 

 or not they are compounds containing nitrogen. You may easily 

 prove in this way that nail parings or human hair cut up fine and 

 mixed with soda-lime will evolve ammonia, and are consequently 

 nitrogenous bodies. Similarly, shreds of woollen cloth and silk 

 will produce ammonia when thus treated ; but threads of cotton 

 and linen, pure paper, calico, and such like vegetable products 

 will not evolve any ammonia on heating with soda-lime, because 

 they are not nitrogenous compounds. 



CHAPTER XIV. 



CHEMICAL ACTIONS OF COMBINATION. 

 Development of Heat. 



In general, wherever chemical combination takes place a more 

 or less considerable development of heat is brought about; the 

 principal sources of artificial heat are in point of fact due to this 

 action, ordinary fires being simply the result of combination of 

 the oxygen of the air with certain bodies of the " combustible " 

 class, e.g., wood, charcoal, coal, oil, tallow, &c. In such cases, the 

 heat produced is not as great as it is when pure oxygen is used 

 instead of air, because the action is somewhat retarded owing to 

 the presence of the inert nitrogen ; accordingly, to produce the 

 highest degrees of artificial heat by means of such actions, pure 

 oxygen is employed, one of the hottest known flames being pro- 

 duced by using hydrogen gas as the combustible substance, and 

 supplying the flame with oxygen. Platinum, a metal almost 

 impossible to melt in a furnace heated by any other kind of flame, 

 can be melted in large quantities at a time in a suitable vessel 

 (made of quicklime) heated by the oxyhydrogen flame (Expt. 

 211), i.e., a flame produced by supplying a jet of hydrogen with 

 the right quantity of oxygen requisite to burn it all to water vapour 

 or steam. 



