Mr. De la Rue on Cochineal. 479 



Several combustions of the carminic acid thus purified were 

 made, the resulting numbers however became useless by the 

 subsequent observation that this acid was by no means pure. 

 A sufficient quantity being incinerated left a residue of acid 

 reaction, which was suspected to contain phosphoric acid. 

 Carminic acid burning only with great difficulty, it was re- 

 converted into carminate of lead, the oxide of lead dissolved 

 out of the residue obtained after fuming by acetic acid, which 

 left a white residue of metaphosphate of lead, together with a 

 little lead. The white residue was soluble in dilute nitric 

 acid, and exhibited, when treated before the blowpipe, the 

 characters of metaphosphate of lead; other tests likewise 

 confirmed the presence of phosphoric acid. It will hereafter 

 be seen that the process of extracting the colouring matter by 

 alcohol (D) does not exclude the phosphoric acid, which in 

 all probability existed in the colouring matter analysed by 

 Pelletier. It is further evident that the presence of phos- 

 phoric acid explains most satisfactorily the facts observed by 

 Arppe. 



a. In order to separate the phosphoric acid, another por- 

 tion of crude carminic acid (A) was precipitated with acetate 

 of lead. Three-fourths of the carminate of lead produced were 

 decomposed by hydrosulphuric acid and evaporated to dry- 

 ness in the way already mentioned. The dry mass being dis- 

 solved in cold absolute alcohol, and filtered from a slight floc- 

 culent brownish residue, was heated to ebullition in a water- 

 bath and mixed with the remaining fourth of the carminate 

 of lead, which had been previously reduced to a fine powder ; 

 the ebullition was continued for a few hours. In this method 

 the free phosphoric acid combined with the lead, liberating 

 an equivalent proportion of carminic acid, which was taken 

 up by the alcohol. The alcoholic solution was filtered whilst 

 hot, concentrated by distillation, and then evaporated in vacuo 

 in the presence of sulphuric acid; it dried into a granular 

 mass of a deep purple-brown colour, detaching itself sponta- 

 neously from the sides of the vessel, and on examination by 

 the microscope was found to be a beautiful transparent crim- 

 son substance, exhibiting only slight, if any, signs of crystal- 

 line structure ; by pulverization it became of a fine scarlet 

 colour ; it left a mere trace of ash, and was found to be per- 

 fectly free from phosphoric acid. It was highly hygrome- 

 tric*. 



* In consequence of this it was found convenient to dry the carminic 

 acid intended for analysis in little stoppered tubes in tlie air-pump, as tlie 

 stopper could be rapidly inserted after desiccation, and access of air effec- 

 tually prevented. 



