Mr. De la Rue on Cochineal, 481 



The last preparation {d) appearing to contain more than 

 any of the others, it was chosen and burnt with soda-lime. 



It was indispensable in experiments of this nature to test 

 the purity of the soda-lime as regarded the absence of am- 

 monia. A tube having 9 inches of its length filled with soda- 

 lime was heated to redness, just as in a nitrogen determi- 

 nation ; the hydrochloric acid, being treated with bichloride 

 of platinum in the usual manner, gave 7'5 milligrammes of 

 ammonio-chloride of platinum ; and a repetition of the expe- 

 riment gave a similar result. This allowance has been made 

 on all the nitrogen determinations by soda-lime. 



•5938 grm. carminic acid {d) gave '0717 grna. ammonio- 

 chloride of platinum = 0*76 per cent, of nitrogen. 



This quantity of nitrogen could not be supposed to belong 

 to the composition of the colouring matter, but was evidently 

 due to some foreign substance, and not improbably to am- 

 monia. In order to purify the carminic acid still more, the 

 same specimen {d) was dissolved in a small quantity of boil- 

 ing absolute alcohol and the filtered solution mixed with three 

 times its bulk of anhydrous aether ; a splendid scarlet precipi- 

 tate was immediately produced, which absorbed water rapidly 

 from the atmosphere, and agglutinated into a dark purple 

 mass ; when dried it weighed 0*3 grm. (e). The filtrate, 

 which was of a pale orange-red colour, left on evaporation 

 0*5 grm. of carminic acid (/"). 



•2635 grm. (e) burnt with soda-lime gave '0637 grm. am- 

 monio-chloride of platinum = 1*52 per cent of nitrogen. 



•4732 grm. (/) gave "0150 grm. ammonio-chloride of pla- 

 tinum = 0^2 per cent, of nitrogen. 



We have therefore (e) 0*3 grm. found to contain by ana- 

 lysis 1^5 per cent, nitrogen, and (/) 0^5 grm. 0^2 per cent., 



(3 X 1-5) -I- (5 X 0^2) ^„ . u- 1, 



^ = '69 average per cent., which agrees 



o 



closely with '76, found previous to treat]Tient with eether. 



(/. Another preparation of carminic acid was obtained 

 by precipitating crude carminic acid with acidulated acetate 

 of copper, which salt was found to carry down the carminic 

 acid, and to leave in solution by far the greater portion of the 

 phosphoric acid. The carminate of copper, which occupied 

 a long time in washing, was collected and decomposed by 

 hydrosulphuric acid. The filtrate was evaporated to dryness, 

 dissolved in boiling absolute alcohol, filtered, concentrated 

 by distillation, and again evaporated to dryness in vacuo. It 

 still contained a trace of phosphoric acid. On evaporating 

 the mother-liquor and filtering, from an impure carminate of 

 copper which deposited as the acetic acid was driven ofi^, and 



Phil. Mag. S. 3. No. 2 11 . Suppl. Vol. 3 1 . 2 1 



