384 Chemical Society. 



by putrefaction. It is astonishing that a substance which so pow- 

 erfully resists the action of chlorine, should be so easily affected by 

 simple contact with putrefying matter. 



A glance at the composition of hippuric acid will show that this 

 change is altogether different from that which urea suffers under 

 similar circumstances, the assimilation, namely, of the elements of 

 water by which it becomes carbonate of ammonia. Hippuric acid, 

 on the contrary, seems to pass into benzoic by an absorption of 

 oxygen from the air, carbonic acid and ammonia being at the same 

 time produced. 



Hippuric acid .... C 18 H 8 N 5 

 Subtract — Benzoic acid C H H 5 3 



C 4 H 3 N O s 



which by addition of 6 eq. of oxygen from the air, would furnish 

 1 eq. ammonia and 4 eq. carbonic acid. 



May 3. — The following communication was made : — 



"On a curious Formation of Prussian Blue," by Robert Por- 

 rett, Esq. 



Mr. Porrett was led to attend to this subject by an observation 

 accidentally made while walking in the garden of a friend. He 

 found that a great number of the pebbles in the gravel walk were 

 tinged of a fine bright blue colour ; and on remarking the appear- 

 ance to the owner, and inquiring as to the cause, though it had 

 never before attracted notice, he ascertained that before the fresh 

 gravel had been laid down, the walks had been strewed with some 

 refuse lime from the gas-works, for the purpose of destroying the 

 worms, and over which the red gravel of the neighbourhood of 

 London had been placed only a few weeks before the appearances 

 described were observed. 



The blue colour was entirely confined to the upper surface of the 

 pebbles which was exposed to the atmospheric air, and was found to 

 be Prussian blue. The pebbles affected were siliceous, having a 

 white exterior coating. Mr. Porrett considers this production of 

 Prussian blue to have arisen from some of the gas-lime having been 

 ' dropped accidentally on the surface of the new gravel, and that the 

 peroxide of iron there found had been deoxidized by some of the 

 sulphur compounds contained in the gas-kme, giving rise to the 

 formation of a combination of iron with cyanogen, also present in 

 the Ume, and calcium, and that this compound had been decomposed 

 by the action of the carbonic acid of the atmosphere, or by the 

 siliceous matter of the stone, and thus causing the formation of the 

 Prussian blue*. 



May 17. — The following communications were read : — 



Extract from a letter from Professor Clark. 



" The burner is to be fixed into a table by screwing thereto the cir- 



[* On a subject allied to that of Mr. Porrett's paper, see Phil. Mag., 

 S. 3. vol. x. p. 329, and also the notice referred to, p. 333.] 



