474 Mr. De la Rue on Cochineal. 



Carbon 49'33 



Hydrogen 6'66 



Nitrogen 3*56 



Oxygen 40*45 



100-00 



M. Pelletier stated, however, that he did not greatly rely 

 on the correctness of this analysis. 



After alcohol had dissolved out all the colouring matter 

 removable by it, they extracted the last traces, by repeatedly 

 M'ashing the residue with boiling water, and along with it a 

 little fatty and some nitrogenous matter ; the residue was a 

 brownish transparent mass. The later decoctions, contain- 

 ing no red colouring matter, left likewise on evaporation a 

 brownish transparent mass, which they considered identical 

 with the organic residue of the insect. This animal matter 

 had, according to them, some analogy with gelatine, but dif- 

 fered in many of its properties, as it did also from albumen 

 and fibrine, they therefore considered it as peculiar to the 

 cochineal insect; the alkalies and ammonia dissolved it 

 readily ; chlorine precipitated it ; all acids and acid salts pre- 

 cipitated it, as also acetate of lead, salts of tin and copper, and 

 nitrate of silver ; and they considered the latter reagent as a 

 good test of the purity of the colouring matter, as it did not 

 precipitate the latter if free from nitrogenous substances. If 

 the colouring matter were contaminated with nitrogenous sub- 

 stances, all the salts which precipitated the latter carried down 

 likcAvise some of the colouring matter. 



An examination of the ashes showed the presence of phos- 

 phate of lime, carbonate of lime, chloride of potassium, and 

 phosphate of potash, to the extent of 0'7 per cent. 



In the second part of the memoir they went into the theory 

 of the technical applications of the colouring matter : this 

 having no reference to the present subject, I do not think it 

 necessary to reproduce it here. 



M. Lassaigne, in 1819*, examined Kermes {Coccus ilicis), 

 an insect common in the South of Europe, and employed as 

 a red dye before the discovery of America, and obtained by 

 following the methods of Pelletier and Caventou, substances 

 agreeing in their properties with the analogous ones found in 

 cochineal. 



M. F. Preissert, in an elaborate paper on the origin and 

 nature of colouring matters, has again drawn the attention of 

 chemists to the subject. This gentleman, from a study of a 

 variety of colouring substances, comes to the conclusion that 

 all resemble indigo in its behaviour with reducing agents. 



* Journal de Pharmacie, ser, 2, tome v. p. 435. f Ibid, p. 191. 



