142. COMBUSTIBLE ACIDS. 



all excess of ammonia was driven off. 17-370 

 grains of crystallized protosulphate of iron were 

 dissolved in water, the oxide was peroxidized, 

 and the solution rendered neutral precisely in 

 the manner described in the last section. These 

 two solutions being mixed, a double decomposi- 

 tion took place, and benzoate of iron immediate- 

 ly precipitated in buff coloured flocks. This 

 precipitate was separated by means of a double 

 filter. The liquid which passed through was 

 transparent and colourless, and was not in the 

 least altered by prussiate of potash, nor was any 

 precipitate occasioned by the addition of persul- 

 phate of iron, showing that it contained no sen- 

 sible quantity of iron, or of benzole acid. 



From this experiment we learn that 15 grains 

 of benzoic acid just neutralize 5 grains of per- 

 oxide of iron. And as 5 represents the atomic 

 weight of peroxide of iron, 15 must be the ato- 

 mic weight of benzoic acid. 



of 2. The benzoate of iron formed in the pre- 

 ceding experiment being dried in the tempera- 

 ture of 212, weighed exactly 20 grains. It was 

 therefore anhydrous, and consisted of 



1 atom benzoic acid 15 



1 atom peroxide of iron 5 



20 



Jlence, the fourth part of this precipitate is per- 

 oxide of iron and the other three-fourths ben- 

 is 



