Alum Mordants. 449 



feined which gives darker colours than the common solu- 

 tion of alum. With this object in view, dissolve 32 lbs 

 alum m 80 lbs. boiling water, and add gradually a hot solu- 

 tion of lllbs. crystallized carbonate of soda in 80 lbs of 

 water, and continue the heat as long as any white flocks 

 remain .in the solution, which will at last disappear with 

 etfervescence. This mordant cannot be printed, as it does 

 no .th,cke n with starch. It does not give dark colours 

 but only light grounds. Hence, the mordant is not fitted 

 for superseding the acetate of alumina, as is stated in 

 many works on dyeino-. 



When the calico is first boiled, with tan or nutgalls, and 

 then impregnated with this mordant, the colours produced 

 are a little darker. ] 



Acetate of alumina mordant .—Tins mordant is formed by 

 mixing the solution of alum with sugar of lead. The quan 

 tity of sugar of lead should always be equal to that of the 

 alum, as it has been found that this proportion, by which 

 much alum remains undecomposed, gives the clearest red 

 and yellow colours. 



Calico takes up a greater quantity of mordant from a so- 

 lution of the acetate of alumina, than from an equally 

 strong solution of alum. When the calico is rinsed after 

 remaining equally long in both solutions, and before beino- 

 dried, the effect of the sugar of lead may be exhibited by 

 applying two mordants, one consisting of 1 lb. alum, and 

 40 lbs water; and the other of 1 lb. alum, 40 lbs. water 

 and lb. sugar of lead; and dyeing the cloth in the same 

 madder solution. The second is darker and clearer than 

 the first. 



_ Th* cause 1 of this difference depends on the circumstance 

 that the acetic acid does not combine so firmly with the 

 alumina as the sulphuric acid; hence the calico, which here 

 acts as an acid, can take up more. It is also possible bv 

 means of acetate of alumina mordant, to fix still more alu 

 mina upon the calico, by allowing the cloth saturated with 

 it to dry By this means a portion gives out acetic acid 

 (which does not occur with sulphuric acid, when alum 

 alone is employed), and the calico is then so strong mor 

 danted, that it pives a very dark red with madder 



VOL. HI. 



2 r; 



