Cochineal Red. 451 



them to boil together, otherwise the sulphate of lead does 

 not precipitate all the Prussian blue. 



As the acetate of alumina becomes flocky by boiling;, the 

 sugar of lead should not be added to the boiling solution 

 of alum ; but it should first be allowed to cool, or what is 

 still better, the alum may be dissolved in one half of the 

 water to be employed, and the other half added in the cold 

 state, when the prussiate of potash has finished its action. 

 By this means the solution will be sufficiently cooled, and 

 the sugar of lead can be added without injury to the solu- 

 tion. 



RED FROM COCHINEAL AND ALUM MORDANT. 



This colour is of little value, as it is not sufficiently clear. 

 Its exhibition on the calico is also attended with many diffi- 

 culties. The solution must be made with water, completely 

 free from lime, otherwise a great part of the cochineal is 

 subtracted, the colouring matter combining with the lime, 

 and becoming insoluble. 



Properties of cochineal red.— This colour is very unstable. 

 It does not withstand the action of light and air. Boiled 

 soap-suds, which contain 1 lb. of soap dissolved in 200 lbs. 

 of water, make the colour half as dark, while they become 

 dark red. It therefore does not stand washing with soap. 



Potash forms brown spots, which are again restored by 

 vinegar. 



Ammonia makes the colour paler, and dissolves it. 



Lime juice forms yellow spots, which are not completely 

 removed by ammonia. 



Vinegar does not alter the colour. 



Solution of chloride of lime bleaches the red very quickly, 

 and leaves a white pattern. 



Tin mordants, No. 1, and 2, only remove the colour par- 

 tially, and hence they cannot be employed to discharge it. 



RED FROM FERNAMBUC AND ALUM MORDANT. 



A light red is obtained by impregnating the cloth with 

 the alum mordant, No. 3, by dipping, pressing, and rinsing. 

 To form a dark red, alum mordant, No. 1, is used, by dip- 

 ping it equally, and allowing the cotton to dry. 



The Mordanted Cloth is purified by rinsing it in running 

 water. 



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