404 Mr. George on the Colouring Matter of Lac. [June, 



tion of tin are poured in ; a moment after ]0}^ lbs. of tartar, and 

 4 lbs. of young fustic in chips, inclosed in a bag, are added, and 

 the whole boiled five minutes. The fire in the furnace is then 

 withdrawn, or smothered, and 20 gallons of cold water poured 

 into the dyeing vessels, 10,', pints of solution of tin are imme- 

 diately added, and the cloths are entered, turning over the 

 winch during ten minutes rapidly, the fire is then raised, and the 

 cloth turned more slowly ; the liquor in the dyeing vessel is made 

 to boil as soon as possible, and the cloths are boiled one hour; 

 they are tlien carried to the river and well washed, and afterwards 

 washed in a fulling stock with water alone. 



These proportions will dye a brilliant scarlet, inclining slightly 

 to the blue tint ; if more of an orange shade be required, white 

 Florence argol may be substituted for tartar, and more fustic 

 used. 



The cloths described weighed 12 ounces to the yard ; heavy 

 stout goods do not require so much of any of the dyeing stuft'in 

 proportion ; since they are not so easily penetrated by the 

 colouring matter, 10,^ lbs. oflacdye will dye 140 lbs. of coating, 

 24 ounces to the yard. 



A scarlet equally brilliant with that dyed in the large way may 

 be produced in small experiments ; in the latter case, the propor- 

 tions are a little different. 1 have found that for the dyeing of 

 180 grains of yarn, in a tin vessel of the capacity of six pints, 

 60 grains of lac dye mixed with 40 grains of lac spirit and 40 

 grains solution of tin, and in the dyeing vessel 70 grains of 

 tartar, 1 dram (measured) of solution of tin and 12 grains of 

 young fustic, produced a brilliant scarlet. 



Lac dye may be substituted for cochineal in most shades of 

 orange, but in the more delicate shades of rose and pink, the 

 large proportion of acid employed to dissolve the lac dye 

 destroys the brilliancy of the colour. I have found in some 

 experiments made with the colouring matter of lac in a state of 

 purity, that all the colours for which cochineal is usually 

 employed may be obtained from it. In lac dye, the colouring 

 matter being combined with alumina, the insolubility of the 

 compound prevents any combination between it and the fibres 

 of wool. Yarn boiled one hour, with a considerable proportion 

 of a lake formed by precipitating the colouring matter of lac 

 from its solution by alumina, scarcely received a stain. 



The sulphuric and muriatic acids are employed to dissolve the 

 alumina ; the colouring matter being thus rendered soluble unites 

 Avith the oxide of tin in consequence of superior affinity, and the 

 new compounds combine with the woollen fibre. It is probable 

 that scarlet dye is a compound of tartrate of tin, or tartrate of 

 potash and tin with colouring matter, since it is only on this 

 supposition, that the eft'ect produced on the colour by the quantity 

 or quality of the tartar employed, can be accounted for. 



