ANNALS 



OF 



PHILOSOPHY. 



JUNE, 1826. 



Article I. 



Experiments on the Colouring Matter of Lac, and on its Applica- 

 tion to the Dyeing of Scarlet. By E. S. George, Esq. FLS. 



(To the Editors of the Annals of Philosophy/.) 



GENTLEMEN, St. Peter's Hill, Leeds, jipril26, 1826. 



Dr. Bancroft was the first to call the attention of the dyers 

 of this country to the use of lac as a colouring matter ; his expe- 

 riments made upon the preparation known as lac lake, appear to 

 have failed in the practical details, yet they led to more success- 

 ful trials, and lac lake was much employed in the dyeing of 

 scarlet upon the coarser woollen cloths. 



But a subsequent improvement in the manufacture in India, 

 imported as lac dye, has furnished us with a dye rivalling cochi- 

 neal in brilliancy, and surpassing it in permanency ; it is to the 

 latter substance our attention has been more particularly 

 directed. 



The best kinds of lac dye consist of the colouring matter 

 combined with alumina, and contain a small portion of resin and 

 extractive. 



One hundred grains of lac dye marked D. T. boiled two hours 

 and a half in three measured ounces of water, lost 10 grains. The 

 solution was of a light yellow colour, and gave with muriate of 

 tin a plentiful fawn-coloured precipitate. When concentrated, 

 the solution became deep-yellow coloured, and had an intensely 

 bitter taste. 



The part insoluble in water was almost entirely dissolved in 

 solution of subborate of soda, or subcarbonate of soda ; from 

 these solutions sulphuric acid, not in excess, occasioned a dark 

 red precipitate, muriate of tin a bright red, and sulphate of 

 alumina and potash a full crimson. The supernatant fluid, after 

 the precipitation by sulphate of alumina and potash, was limpid; 

 after that by muriate ot tin, peach-coloured ; and after sulphuric 

 acid, light-orange. 



New ISeries, vol. xi. 2 u 



