VII.] COMPOSITION OF PURE WATER. 105 



conditions, water may be resolved into its elements by the 

 application of heat alone, just as it may be decomposed 

 by means of electricity. This interesting fact was discovered 

 by Sir W. R. Grove, more than thirty years ago. He found 

 that if a piece of the metal platinum, such as a small solid 

 ball, be made white hot, as may be done by the intense 

 heat of the oxy-hydrogen blowpipe, and then be suddenly 

 plunged into water, the liquid is at once decomposed into 

 its constituent gases. But although this process is of great 

 theoretical interest, it is not one which in the present state 

 of science can be advantageously applied to the decom- 

 2:)Osition of water. 



Having obtained oxygen and hydrogen by the decom- 

 position of water, it may naturally be inquired whether 

 these substances cannot in turn be decomposed. To this 

 question it can be simply replied that the most skilful 

 chemists have hitherto failed to effect such decomposition. 

 They have found it impossible to obtain from oxygen 

 anything but oxygen, or from hydrogen anything but 

 hydrogen ; and, in the present state of our knowledge, these 

 bodies are consequently regarded as elementary ox simple sub- 

 stances. Nitrogen, which was obtained from the atmosphere 

 (p. 79), is another of these elements ; and altogether chemists 

 are acquainted with no fewer than sixty-five of these simple 

 bodies, a large proportion of which are metals. Everything 

 existing around us is consequently regarded by chemists 

 either as an element or as a compound. Oxygen, hydrogen, and 

 nitrogen are elements ; carbonic acid, ammonia, and water 

 are compounds. These compounds generally have proper- 

 ties very different from those of their constituents ; thus, in 

 none of its physical forms, does water possess the properties 

 of either hydrogen or oxygen ; even as steam, it differs 

 markedly from these, being neither combustible like the 



