70 Royal Institution* 



formation of chloride of copper, CuCl-, is G0'5 units. Hence, with 

 chlorine in solution and excess of both copper and zinc, there is 

 finally produced the maximum possible amount of chloride of zinc 

 and no chloride of copper. 



Again, ou addition of sufficient zinc to solution of chloride of cop- 

 per, there is complete combination of chlorine with zinc and complete 

 separation of chlorine from copper, I. c. complete burning- of the one 

 metal and complete unburning of the other. 



IV. 



But under simpler though less familiar conditions, chemical action 

 habitually takes place in more than one direction simultaneously, 

 with production of correlative products in varying proportions. 



Thus, with hydrogen and excess of both chlorine and oxygen, 

 although the heat of formation of oxide of hydrogen, H J O, is 57 

 units, and the heat of formation of chloride of hydrogen, 2HC1, is 

 only 47*5 units, yet in this case the hydrogen does not combine with 

 the oxygen to the exclusion of the chlorine, but divides itself between 

 the oxygen and the chlorine in proportions which vary with the con- 

 ditions of the experiment. 



In accordance with this result it is found that, at the same red 

 heat, exeess of chlorine will effect the partial decomposition of water 

 with extrusion of oxygen, and, conversely, that excess of oxygen 

 will effect the partial decomposition of hydrochloric acid with extru- 

 sion of chlorine. 



So that, beginning with the two chemical substances water and 

 chlorine, or beginning with the two chemical substances hydrochloric 

 acid and oxygen, or beginning with the three chemical substances 

 hydrogen, chlorine, and oxygen, there exist at a full red heat the four 

 chemical substances, water, hydrochloric acid, chlorine, and oxygen — 

 the proportions of the four substances depending certainly upon the 

 relative quantities present of the elements concerned, and most pro- 

 bably also upon the temperature of the experiment. 



Similarly, beginning with the one chemical substance water 

 (Grove), or beginning with the two chemical substances oxygen and 

 hydrogen (Bunsen), there always exist at a sufficiently high tempe- 

 rature the three chemical substances water, oxygen, and hydrogen. 



Although, by exposure to a red heat, the electrolytic mixture of 

 oxygen and hydrogen gases becomes completely combined or trans- 

 formed into water, yet, as recently shown by Bunsen, at the high 

 temperature of '2024° only one-half, and at the still higher tempera- 

 ture of 2844° only one-third of the mixture undergoes combination, 

 the other one-half or two-thirds remaining in the state of mixed gas. 



V. 

 Chemists are acquainted with many reciprocal actions comparable 

 with those of chlorine upon water, and of oxygen upon hydrochloric 

 acid, the most familiar instance being probably the decomposition of 

 ignited oxide of iron by hydrogen with extrusion of iron, and the 

 converse decomposition of oxide of hydrogen by ignited iron with 

 extrusion of hydrogen. 



