308 BONELLEIN. CARMINIC ACID. [BOOK I. 



2. Alcohol solutions, slightly acidulated 



636, 611, 588, 565, 543, 522, 492. 

 31 strongly acid 



617, 590, 565, 552, 517. 

 Solutions of Bonellein are fluorescent. 



Carminic acid. 



The female Cochineal insect (Coccus cacti) contains from 26 

 50 p. c. of a splendid red colouring matter, to which the name of 

 Carminic acid is given, and from which commercial carmine is pre- 

 pared. This colouring matter is found in other species of Coccus, 

 and occurs in the vegetable kingdom, being found in the blossoms of 

 Monarda didyma. 



Mode of One part of powdered cochineal is boiled in 40 parts 



preparation. of water for half an hour; the solution is then decanted, 

 precipitated with lead acetate, care being taken to avoid an excess of 

 the precipitant ; the precipitate is washed with boiling water so long 

 as the washings give a precipitate with solutions of mercuric chloride ; 

 it is then decomposed by sulphuretted hydrogen; the filtrate from 

 the precipitate of lead sulphide is evaporated to dryness at a very low 

 temperature, and the residue is extracted with alcohol, which dissolves 

 the carminic acid. 



Composition Carminic acid, C 17 H 18 O 10 , is an amorphous red powder 



and proper- easily soluble in water, and alcohol, and in hydrochloric 

 ties. an d sulphuric acids. It forms no salts of constant com- 



position. The ammonium salt exhibits two absorption bands between 

 D and E nearer E than those of oxy-haemoglobin ; these bands are 

 more closely approximated than those of oxy-haemoglobin and have 

 less distinct edges. Aqueous and alcoholic solutions of cochineal 

 on the other hand absorb all but the red rays. 



The author has determined the position of the centres of the two bands 

 of carminate of ammonia. The centre of the band which corresponds to 

 that designated as a in the spectrum of oxy-haemoglobin is approxi- 

 mately 530, the centre of the band corresponding to the band /? of 

 oxy-haemoglobin is approximately 570. An ammoniacal solution of carmine 

 ulso exhibits two absorption bands, of which the centres are respectively 570 

 and 528. 



A solution of picro- carmine exhibits a spectrum which at first sight very 

 closely resembles that of oxy-haemoglobin. It will be observed, however, 

 that the band near the red (a) is less dark than the one in the green, the 

 centres being respectively approximately 565 and 520, and there is a third 

 band in the blue, very close to its junction with the green. 



Carminic When boiled with dilute acids carminic acid 



acid a Giuco- combines with the elements of water to form an 

 side - unfermentable sugar, which is optically inactive, and a 



new pigment carmine-red (C n H 12 O 7 ) : 



C,,H 18 W + 2H,0 = C 6 H 10 5 + C U H 12 7 . 



