CRUSTACEA. 123 



when exposed to a heat of 70 (centigrade), and in 

 this state resembles the red colouring matter ex- 

 tracted by Goebel from the legs and beaks of 

 certain geese and pigeons. It can be extracted 

 from the lobster's shell by means of alcohol, in 

 which it is soluble ; but during the operation the 

 colour turns red. Sulphuric and nitric acids turn 

 the red alcoholic solution to a permanent green, 

 which the alkalis do not again change to red. 

 This is one of its most remarkable properties. A 

 permanent organic green is such a desideratum at 

 this moment in the tinctorial world, that the dis- 

 covery of a new dye of that description would be 

 worth thousands of pounds ! 



Moreover, the red colour of the lobster can be 

 modified by chemical means; for instance, with 

 oxide of lead it produces a violet combination, and 

 the dark-coloured shell becomes red when it is put 

 in contact with acids, alkalis, certain salts, etc. It 

 also turns red by long exposure to the air, by 

 putrefaction, etc. ; but it does not change colour in 

 carbonic acid gas, or in hydrogen. Chlorine 

 bleaches it completely. 



The hard envelope of Crustacea is formed prin- 

 cipally of carbonate of lime, a little phosphate of 

 lime, and a few other salts in small proportions. 

 All these are intimately mixed with a certain 

 amount of animal tissue. 



