116 COMBINING PROPORTIONS. 



the original salts disappear completely and two new salts are 

 produced, the sulphate of barytes which is insoluble and preci- 

 pitates, and the nitrate of magnesia which remains in solution, 

 as represented in the following diagram in which the equivalent 

 quantities are expressed : 



Before decomposition. After decomposition. 



759 sulphate (258 magnesia . 935 nitrate of 



of magnesia 1501 sulphuric acid . magnesia. 



1634 nitrate J 6' 7 7 nitric acid 

 of barytes \ 957 barytes 



1458 sulphate 

 of barytes. 



After a double decomposition of this kind, the liquid remains 

 neutral, or there is no redundancy of either acid or base, because 

 each of the new salts is composed of a single equivalent of 

 acid and of base like the salts from which they are formed. If 

 one of the salts be added in a larger proportion than its equi- 

 valent quantity the excess does not interfere with the decom- 

 position, and remains itself unaffected, the decomposition pro- 

 ceeding no farther than the equivalents present. Hence the 

 general observation that neutral salts continue neutral after 

 decomposition, in whatever proportions they may be mixed. 



But the modes of fixing the equivalent numbers which have 

 been stated are inapplicable to several elementary bodies, such 

 as nitrogen, phosphorus, carbon, boron, silicon and some me- 

 tals, of which the protoxides are not bases and are uncertain. 

 Nitrogen enters into nitric acid, of which acid it is known that 

 the equivalent is 677? and that it contains five equivalents or 

 500 parts of oxygen, and consequently 177 parts of nitrogen. 

 It is doubtful, however, whether 1 77 represents one or two 

 equivalents of nitrogen. But the equivalent of ammonia like- 

 wise contains 177 nitrogen, and a less proportion is never found 

 in the equivalent of any other compound into which that ele- 

 ment enters. The number 177 is? therefore, the least combining 

 proportion of nitrogen, and must on that account be taken as 

 one equivalent. The equivalent of phosphorus can be shown 

 on the same principle to be 392.28, that of arsenic 940.08 and 

 that of antimony 1612.90, as given in the tables, and not the 

 halves of these numbers as commonly estimated. These three 

 bodies agree with nitrogen in their chemical relations, and the 

 numbers recommended represent the quantities which replace 



