1821.] Atomic Weight of various Metals and Acids. 141 



the liquid scarcely reddened vegetable blues, taking care not to 

 precipitate any of the iron. 



The two solutions thus formed were mixed together. A 

 copious brick red precipitate immediately separated ; indeed, it 

 was so abundant (owing to the concentration of the liquids), 

 that it did not speedily subside. The whole was, therefore, 

 thrown upon a filter. The liquid which passed through was 

 transparent and colourless. It was tested for iron and benzoic 

 acid by prussiate of potash and persulphate of iron ; but was not 

 affected by either of these reagents. We see from this that 15 

 grains of benzoic acid are exactly neutralized by five grains of 

 peroxide of iron ; consequently an atom of benzoic acid weighs 

 • 15, and the crystals of this acid contain no water. 



XI. Succinic Acid. 



This acid being obtained by sublimation, as well as the ben- 

 zoic, is probably destitute of water ; but in its usual state, it is 

 contaminated by a good deal of oil. In the acid which I em- 

 ployed for my experiments, this oil had been removed by digest- 

 ing it in nitric acid. It was quite white, and crystallized in 

 small four-sided prisms. From Berzelius's experiments, the 

 weight of this acid was probably 6*25. 



To verify this opinion, 6-25 grains of the crystals were dis- 

 solved in water neutralized by ammonia, and mixed with a solu- 

 tion of 17-375 grs. of protosulphate of iron, peroxidized and 

 neutralized by the very same method which was followed in the 

 case of benzoic acid. The two solutions were mixed together, 

 and the whole was thrown on a filter. The persuccinate of iron 

 remained on the filter in the state of a fine red matter. The 

 liquor which passed through the filter was transparent and 

 colourless, and, when tested with prussiate of potash and per- 

 sulphate of iron, it gave no indication of containing either iron 

 or succinic acid. From this experiment, it follows that succinic 

 acid weighs 6*25, and that the crystals of it contain no water of 

 crystallization. 



Perbenzoate and persuccinate of iron, when dried at the tem- 

 perature of 212°, contain no water. They furnish, therefore, an 

 easy method of analyzing the benzoates and the succinates ; for 

 a benzoate, we have to multiply the weight of perbenzoate of 



15 3 

 iron obtained by -, or -, or 0-75, the product is the weight of 



benzoic acid ; while -, or 0*25, gives the weight of peroxide of 

 iron ; for a succinate, we must multiply the weight of persucci- 

 nate of iron by rr-^r, or 0*555, the product is the weight of suc- 

 cinic acid. If we multiply the weight of persuccinate of iron by 



