Mr. De la Rue on Cochineal. 485 



produce purple precipitates ; all the alkaline earths produce 

 purple precipitates ; sulphate of alumina gives no precipitate, 

 but on addition of a drop of ammonia the carminic acid is 

 immediately taken down as a beautiful crimson lake ; acetates 

 of lead, copper, zinc and silver give purple precipitates ; the 

 latter is immediately decomposed, and silver deposited ; the 

 nitrates of lead, mercury and silver reddish precipitates ; pro- 

 tochloride and bichloride of tin no precipitates, but change 

 the colour to a deep crimson. 



The acid character of carminic acid being so very little pro- 

 nounced, I met with considerable difficulties in determining 

 its atomic weight ; it is only with great reserve that I bring 

 forward the formula before cited. Several attempts were 

 made to produce soda, baryta, lead and copper compounds, 

 but it was only with the copper salt that I obtained results 

 agreeing in different preparations. 



It seems that carminic acid attaches itself to salts, for it 

 was found that the precipitants could be removed from the 

 precipitates only with the greatest difficulty. I omit several 

 soda, baryta and lead determinations which have not led to 

 any satisfactory result, and confine myself to the statement of 

 the result of the analysis of the copper compound. It was 

 obtained by acidulating an aqueous solution of pure carminic 

 acid with acetic acid, and then precipitating by the cautious 

 addition of acetate of copper, so as to leave an excess of car- 

 minic acid in the liquid. The precipitate was well-washed by 

 decantation (by which a great loss was sustained) and dried. 

 It formed into masses of a bronze colour, very hard and dif- 

 ficult to powder. Two specimens were prepared at different 

 times (« and b). 



I. -2800 grm. (a) dried at 100° C. left, after ignition and 

 treatment with nitric acid and re-ignition, '0330 grm. oxide 

 of copper. 



II. -3782 grm. (b) dried at 100° C. gave -0426 grm. oxide 

 of copper. 



III. '4702 grm. (b) dried at 100° C. gave on burning with 

 chromate of lead '8210 grm. carbonic acid and '1743 grm. 

 water. 



These numbers lead to the following per-centage results : — 



I. II. III. 



Carbon ... 47*62 



Hydrogen ... 4*12 



Oxide of copper 11-78 11-27 

 agreeing closely with the formula, C^ H^4 Ojg, CuO, as will 

 be seen from a comparison of the theoretical and experimental 

 numbers. 



