NATURAL COLOURS 447 



example, the wool of the negro and the feather of the rook owe 

 their blackness to the same or to different pigments. But the 

 difficulty of investigations of this kind will be sufficiently illus- 

 trated by reference to one other pigment of animal origin, and 

 that a familiar one. 



Everyone is acquainted with the beautiful water-colour paint 

 carmine, and the red essence of cochineal, which is used in cookery 

 for colouring jellies, etc. The red substance in this case is derived 

 from the body of the cochineal insect (Coccus cacti) which is 

 cultivated in Mexico and in the Canary Islands, collected, dried, 

 and sent into commerce in the form of small silver grey masses 

 about a quarter of the size of small peas. These are the bodies of 

 the females, the males being furnished with wings and have but 

 a very brief existence after development from the larva. From 

 1909 to 1913, according to the statement of the Board of Trade 

 for 1913, the amount of cochineal imported into this country 

 almost entirely from the Canaries was as follows : 



17871269169216231401 cwts. 



This, though a large quantity, is a great falling off from the 

 amount imported in the days when the British army was clothed 

 in scarlet and cochineal was the dye. The red colouring matter 

 has been the subject of experiment since 1813 when it was 

 analysed by Pelletier and Caventou who assigned to it a formula 

 which included the element nitrogen. Arppe and Warren de la 

 Rue examined it again thirty years later and showed that it did 

 not contain nitrogen. Since that time the carminic acid, so named 

 by the last-mentioned chemists, has had half a dozen different 

 formulae attributed to it, of which the one selected by Hlasiwetz 

 and Grabowski in 1867 approximates nearest to the truth. 

 Corrected by Professor A. G. Perkin and Mr. C. R. Wilson it 

 appears that the expression C n H 12 6 , or the double of this, 

 C 22 H 24 12 , certainly represents its composition. Carminic acid 

 is a crystalline compound and yields well-defined salts, and the 

 question as to the order in which its constituent elements 

 are united together in the molecule should not be difficult to 

 answer. The synthetic production even of this colouring matter 

 should be a practical matter for the manufacturer. Whether it 

 would take a permanent place among the numerous red dyes 

 would then be chiefly a question of cost. 



