CHEMISTRY OF THE NINETEENTH CENTLRY, 627 



cerned only with such of the more general aspects of the science, as may 

 be presumed capable of being made intelligible to a general reader. 

 We shall, therefore, bring this chapter to a close by pointing out some 

 methods of chemical research which are daily growing in importance, 

 and appear to indicate the path along which the science is to advance. 

 If hydrogen and oxygen gases be mixed within certain limits of pro- 

 portion, a flame applied to the mixture causes a sudden combination 

 of the gases (attended with light and heat) in one definite proportion, 

 viz., two volumes of hydrogen with one of oxygen. The excess above 



FIG. 315. 



that proportion of either will be left unaltered. The explosion, as the 

 sudden union of the gases is called, may be determined by an electric 

 spark or by a piece of incandescent metal. The spark, indeed, operates 

 only by the heat attending it. This combination of the gases is often 

 effected in the eudiometer invented by Volta. Its construction and use 

 will be obvious from a mere inspection of Fig. 315, which requires no 

 explanation beyond the statement that the eudiometer is here used 

 with mercury contained in a marble trough. We see that heat causes 

 the explosive combination of a mixture of oxygen and hydrogen gases, 

 especially when these gases are mixed in the proportions in which they 



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