446 



AXPENDIX. 



many chemists to attribute the variations to errors of exper- 

 iment, and to regard the law of correspondence of atomic 

 weights as universal. 



313. 



CALCULATION OF FORMULAE. The student interested in 

 the subject will readily devise for himself the reverse pro- 

 cess of calculating formulae from the per centage results of 

 analysis. The formulae obtained must obviously be such, 

 that if reconverted into per cents, the numbers obtained will 

 agree very nearly with the results of analysis. There may 

 sometimes be a doubt whether the simplest formula which 

 will express the composition, or some multiple of it is the 

 true one. This can only be decided by the analysis of one 

 of the compounds of the substance in which the formula of 

 the second constituent is established. 



The reasoning will be best illustrated by an example. It 

 being assumed that neutral salts contain one equivalent of 

 base to one of acid, the analysis of the neutral sulphate of 

 potassa would establish the formula for sulphuric acid, SO, 

 instead of SaOe. KO,SO3 would express correctly the com- 

 position of the salt, while the substitution of SsOe for SsOa 

 in the same formula, would give a double proportion of acid. 



323. 



When the same element unites with oxygen in different 

 proportions to form different acids, these are distinguished 

 by prefixes and terminations, which indicate the order in 

 which they stand to each other, with respect to the quantity 

 of oxygen. 



The first acid of such a series discovered, generally receives 

 the termination " ic." Chloric acid may serve as an exam- 

 pie. Another acid compound of chlorine since discovered, 



