132 Dr. Stenhouse on the 



atomic weights being the same. They are not identical sub- 

 stances, however, and may be easily distinguished, among 

 others, by the following particulars : — Pyromeconic acid gives 

 a fine red with persalts of iron, while pyromucic acid gives 

 only a dirty green colour ; pyromeconic acid does not preci- 

 pitate basic acetate of lead, while pyromucic acid does so ; 

 pyromucic acid reduces oxide of silver, with evolution of gas, 

 as a black powder, while pyromeconic acid precipitates it as a 

 metallic mirror ; lastly, pyromucic acid, when boiled with 

 alcohol and sulphuric acid, forms an aether, this pyromeconic 

 acid fails to do. I may mention also, that I was unable to ob- 

 tain an aether with either meconic or komenic acids. 



Pyromeconic acid may be procured in considerable quan- 

 tity by distilling the acid meconate of copper. This salt falls 

 as a greenish-yellow precipitate when pyromeconic acid is 

 added to acetate of copper. Pyromeconic acid may also be 

 obtained, but in very small quantity, by the distillation of the 

 neutral meconate of copper. This salt has a fine emerald- 

 green colour, and is formed when a soluble salt of copper is 

 treated with meconate of potash. When meconate of lime is 

 distilled it only yields empyreumatic products, without any 

 trace of pyromeconic acid. 



It has already been mentioned that meconic and komenic 

 acids, when distilled, yield small quantities of another acid be- 

 side the pyromeconic. Towards the end of the distillation, 

 when the greater portion of the pyromeconic acid has passed 

 over, a few feathery crystals of this second acid condense on 

 the sides and neck of the retort. This acid was first noticed 

 by Gruner and Robiquet. Berzelius has called it the pyro- 

 komenic acid. This name would be very appropriate if this 

 acid were produced by the distillation of komenic acid alone, 

 but it appears not quite so suitable when we consider that the 

 fixed products of meconic and komenic acids are precisely the 

 same. Dr. Gregory considers this acid to be the komenic 

 acid perhaps regenerated. The best way of procuring it is 

 by sublimation, but even this yields it in very small quantity. 



A portion of meconic acid was introduced into Dr. Mohr's 

 apparatus, and sublimed at as high a temperature as the paper 

 would bear without charring. The greater portion of the 

 pyromeconic acid, which was also formed at the same time, 

 was either destroyed or dissipated, but a little of it, together 

 with the crystals of the second acid, which 1 shall call the pa- 

 rakomenic, were found in the cap and on the diaphragm. The 

 crystals of parakomenic acid may be easily separated from the 

 pyromeconic acid, with which they are mixed, by washing 

 them either with cold water or alcohol, in both of which pa- 



