160 ANIMAL COLOURING MATTERS. 



nal colour of the solution reappears, but if the action of the al- 

 kali be prolonged, or if it be increased by the application of heat, 

 the violet colour is destroyed, and the liquid becomes first red 

 and then yellow. 



Lime-water occasions a violet-coloured precipitate when dropt 

 into the aqueous solution of carmin. Barytes and strontian cause 

 no precipitate, but produce the same change of colour as the alkalies. 

 Alumina has a very strong affinity for carmin. When newly 

 precipitated alumina is put into an aqueous solution of carmin, 

 the liquid is deprived of its colour, and the alumina converted 

 into a beautiful lake. If a few drops of acid be added to the 

 aqueous solution before introducing the alumina, the lake ob- 

 tained has a fine red colour as before, but it becomes violet on 

 the application of the least heat. The same effect is produced if 

 we add to the liquid a few grains of an aluminous salt. 



Most of the saline solutions alter the colour of the aqueous so- 

 lution of carmin, but few of them are capable of throwing down 

 a precipitate from it. Solutions of gold merely/liter the colour ; 

 nitrate of silver occasions no change whatever ; the soluble salts 

 of lead render the colour violet ; and acetate of lead occasions 

 an abundant violet precipitate. By decomposing this precipitate 

 by means of a current of sulphuretted hydrogen, we may obtain 

 the carmin dissolved in water in a state of purity. Protonitrate 

 of mercury throws down a violet precipitate. Pernitrate of mer- 

 cury does not act so powerfully, and the colour of the precipitate 

 is scarlet. Corrosive sublimate produces no effect whatever. 



Neither salts of copper nor of iron produce any precipitate ; 

 but the former change the colour of the liquid to violet, the lat- 

 ter to brown. Protochloride of tin throws down a copious violet 

 precipitate ; while the perchloride changes the colour to scarlet, 

 but precipitates nothing. When gelatinous alumina is added to 

 the mixture, we obtain a fine red precipitate, which is not altered 

 by boiling. None of the aluminous salts occasion a precipitate ; 

 but they change the colour to carmin. The salts of potash, so- 

 da, and ammonia, change the colour of the liquid to carmin red. 



From the action of the different salts on carmin, Pelletier and 

 Caventou have drawn as a conclusion, that the metals suscepti- 

 ble of different degrees of oxydizement act like acids on the co- 

 louring matter when at a maximum of oxidation, but like alkalies 

 when at a minimum or medium degree ; and that this alkaline 





