COMBINING PROPORTIONS. 



of iron and a large class of admitted protoxides. The lower 

 degree of oxidation of copper or the red oxide,, which contains 

 only half the proportion of oxygen in the black oxide, comes 

 therefore to be considered a sub oxide, or a compound of two 

 equivalents of metal and one of oxygen. For reasons somewhat 

 similar the higher of the two grades of oxidation of mercury, 

 or the red oxide of that metal, is now generally acknowledged 

 to be the protoxide or to be composed of single equivalents, 

 and the ash coloured oxide reputed a sub oxide. These sub- 

 oxides of mercury and copper are capable of combining with 

 acids, but they are the only sub- oxides which possess that 

 property. It is the character of protoxides to form salts with 

 acids ; and of several oxides of the same metal, the protoxide is 

 always the most powerful base. 



Bodies likewise replace each other in combination, in equiva- 

 lent quantities. Thus in the decomposition of water by chlo- 

 rine, which occurs in certain circumstances, 442 parts of chlo- 

 rine unite with 12.5 hydrogen or one equivalent of that body, to 

 form hydrochloric acid, and displace at the same time and 

 liberate 100 parts of oxygen. Hence the number 442 repre- 

 sents the combining proportion of chlorine which is equivalent 

 in combination to, or can be substituted for 100 oxygen. Again 

 in decomposing hydriodic acid, 442 chlorine unite with 12.5 

 hydrogen, and liberate 1580 iodine, which proportion of iodine 

 may again acquire 1 2.5 hydrogen by decomposing sulphuretted 

 hydrogen and set free 201 sulphur. Hence 1580 and 201 are 

 the equivalent quantities of iodine and sulphur, which take the 

 place of 442 chlorine or 100 oxygen in combination with 12.5 

 hydrogen. When 403 parts of zinc are introduced into a 

 solution of nitrate of copper, they dissolve, acquiring 100 

 oxygen and 677 nitric acid, and become nitrate of zinc, while 

 396 parts of metallic copper are deposited, which had previously 

 been in the state of nitrate and in combination with the above- 

 mentioned quantities of oxygen and nitric acid, and the solu- 

 tion remains otherwise unaltered. Zinc throws down nearly all 

 the metals from their solutions in acids in the same manner, 

 and if the quantity of this substance introduced into the solu- 

 tions and dissolved, be a combining proportion, as in the 

 instance given, the quantities of the metals precipitated will also 

 be combining proportions of those metals. The quantity of 

 zinc employed may be varied, but the quantity of other metal 



