CANCRTN. 163 



CHAPTER III. 



OF CANCRIN, OR THE COLOURING MATTER OF CRABS. 



IT is well known that the crusts which cover the different spe- 

 cies of Cancer, as the gammarus (or lobster), the astacus (or craw- 

 jisti), &c. are black, or nearly so, but become of a fine red co- 

 lour when boiled. It is evident from this that they contain a 

 peculiar colouring matter. 



Dr John made a chemical examination of the crust of the Can- 

 cer astacus in 1811. * He notices some of the characters of the 

 colouring matter ; but does not seem to have made any attempt 

 to obtain it in a separate state. Lassaigne, in 1820, succeeded in 

 isolating it, and made some experiments on it. f The investiga- 

 tion was carried somewhat farther in 1821 by M. Macaire, who 

 found two different colouring matters in these crusts \ 



The colouring matter of these crusts is analogous to suet. In 

 the natural state its colour is dark bluish-green. When heated 

 to 158 it becomes red, and then has some resemblance to the 

 beak of the duck. It is contained partly in the shell, and partly 

 in the greenish membrane immediately under the shell. Some 

 of it is also to be found in another membrane situated immedi- 

 ately below the green one, and from which it may be separated 

 by maceration in water. But in this second membrane, the co- 

 louring matter is already red. Lassaigne obtained the colouring 

 matter by digesting the clean shell in alcohol till that liquid 

 ceased to extract any thing more. The alcoholic solution is red. 

 When it is evaporated to dryness there remains a solid red mat- 

 ter, similar to suet, which, after having been washed in hot water, 

 may be kept without undergoing any alteration. It is insoluble 

 in water ; but very soluble in alcohol and ether. The alcoholic 

 solution has a scarlet colour, and is not precipitated by water. 

 It is soluble by the assistance of heat in melted tallow, and in 

 the vplatile oils. It is stated by Macaire not to be soluble in the 

 fixed oils. 



It dissolves readily in dilute sulphuric acid, but is decomposed 



* Chemische Untersuchungen, ii. 49. 



f- Jour de Pharmacie, vi. 174 



\ Bibl. Univer., July 1821, or Schweigger's Journal, xxxiii. 257- 



