COMBINING PROPORTIONS. 115 



are its caustic taste and power to restore the blue colour of red- 

 dened litmus, by the following proportions of different acids, 

 and a neutral compound or salt produced in every case : 



Sulphurous acid . . .401 

 Sulphuric acid . . .501 

 Hydrochloric acid . . . 454.5 

 Nitric acid .... 6'77 

 Chloric acid . . . .912 

 Hyperchloric acid . . . 1 142 

 lodic acid .... 2078 

 Hyperiodic acid . . . 2278 



It thus appears that the acids differ as widely among them- 

 selves in their equivalent quantities as the bases do. The equi- 

 valent of either an acid or base thus deduced from its neutral- 

 izing power is always the same as that indicated by its 

 composition, namely the sum of the equivalent numbers of its 

 constituents. As the bases which saturate acids fully are 

 all protoxides, it also necessarily follows that there are always 

 100 parts of oxygen contained in the proportion of base which 

 neutralizes the equivalent of an acid. 



The equivalents of both acids and bases are likewise observed in 

 those decompositions in which one acid is substituted for another 

 acid in combination, or one base for another base. Thus an 

 equivalent of sulphuric acid is found to Disengage the equivalent 

 quantity exactly of sulphurous acid froiii the sulphite of soda, 

 of nitric acid from the nitrate of potash or of hydrochloric acid 

 from the chloride of sodium, and to replace it in combination 

 with the base, forming in every case a neutral sulphate. 

 An equivalent of potash separates in like manner an equivalent 

 of magnesia, of lime, of barytes or of protoxide of lead from its 

 combination with an acid. The proportion of acid or base neces- 

 sary to produce a certain amount of decomposition may there- 

 fore be calculated from a knowledge of the equivalents of 

 bodies, and such knowledge comes to be of the most frequent 

 and valuable application for practical purposes. 



But the substitution of equivalent quantities of different 

 bodies for one another is most strikingly exhibited in the de- 

 compositions which follow the mixture of certain neutral salts. 

 An equivalent of sulphate of magnesia being mixed with an 

 equivalent of nitrate of barytes, the two bases exchange acids, 



i 2 



