WATER. 200 



" I have employed a wire ignited by galvanism, to inflame the hy- 

 drogen in this apparatus, and conceive it to be a much less precari- 

 ous method than that of employing an electric machine, or electro- 

 phorus." Hare. 



(f.) Oxygen and hydrogen may be combined by explosion. This 

 happens of course, in all cases where they are fired together ; the 

 product is lost, if the explosion finds vent into the open air, but if 

 confined to an eudiometer tube, over mercury, a little water will be 

 obtained ; this is never done except for the purposes of eudiometry, 

 which will be mentioned again. 



(g.) Oxygen and hydrogen combine by pressure. -The two gases, 

 will remain forever in mere mixture, at the common temperature 

 and pressure, without combining ; but by sudden and violent com- 

 pression in a syringe, they will explode, probably on account of the 

 heat which is thus evolved, for " an equal degree of condensation, 

 slowly produced, has not the same effect." 



These gases combine slowly above the temperature of boiling mer- 

 cury, and below that of glass when ignited, so as to be just visible 

 in the dark. 



12. PROPORTION OF THE ELEMENTS. 



(a.) By volume, 2 hydrogen, and 1 oxygen, 



by weight, 88.9 oxygen, > , 



-, " 11.1 hydrogen, $ veryi 



The combining weight, if there be one proportion of each, 



Combining weight of water, 9* or 11.25 



(b.) The proportions of the elements in water, have been settled 

 after the most rigorous and often repeated analysis. The atomic hy- 

 pothesis, and the theory of definite and multiple proportions, are built 

 upon the result of this analysis. All chemists take either oxygen or 

 hydrogen for unity, and of late the weight of opinion and authority is 

 evidently in favor of hydrogen. 



WATER ANALYSIS. 



1 . If water, in the state of steam, be passed over clean ignited iron, 

 in an iron, or in a luted glass or earthen tube, the iron absorbs the ox- 

 ygen, and hydrogen gas is obtained ; the weight of the hydrogen 

 added to the increased weight of the iron equals that of the water de- 

 composed. Zinc, antimony, and several other metals will answer the 

 same purpose more or less perfectly. 



The common arrangement for decomposing water is represented 

 by the following figure from Dr. Hare. 



* 9 is the number now generally adopted. 



27 



