Cow Dung. 375 



The decoction of bran speedily sours; it should not, 

 therefore, be prepared long before using it. It often sours 

 during dyeing, especially when the process is long. This 

 is very injurious to the dye ; it is prevented by the addition 

 of chalk, in the proportion of 20 lbs. of bran to lib. of 

 chalk. 



The bran which has been employed for dyeing with mad- 

 der acquires a reddish-brown colour ; and when boiled 

 with spirit of wine, gives up this colouring matter. The 

 quantity of this is, however, so inconsiderable, that the loss 

 will be far outweighed by the favourable action of the bran. 



Cow- dung. — The cow-dung bath has been long employed, 

 and certainly with great propriety, as a method for cleans- 

 ing the printed cotton. Its principal use is to remove the 

 superfluous quantity of mordants, and the substance em- 

 ployed for thickening, which do not adhere to the cotton, 

 and thus prevent them from precipitating upon those por- 

 tions which are unprinted, and are intended to remain 

 white. 



To have a clear notion of the action of cow-dung, it is 

 necessary to be acquainted with its constituents, or those 

 substances which are principally necessary for the object 

 mentioned. 



The active matter of cow-dung can be separated by sul- 

 phate of copper, and its properties ascertained separately. 



Let fresh cow-dung be agitated with twenty times its 

 weight of water, and filtered through fine paper. Let the 

 clear dark-brown solution which passes through, be mixed 

 with a solution of sulphate of copper; a dark-brown preci- 

 pitate results, which, after washing with water, will be deT 

 composed by sulphuretted hydrogen. This separates the 

 copper contained in the precipitate in the form of sulphu- 

 ret of copper, and a clear brown solution is obtained, which 

 reddens litmus strongly; and, when evaporated, leaves a 

 dry brown mass, which tastes acid and astringent. This 

 mass, which consists of a brown colouring matter, and a 

 very strong colourless acid (Bosoprine and Bosopric acid*), 

 is, therefore, the efficient means of purifying the mordanted 



* I have snlriitulfil these tonus for the cow-dung brown, and cow-dung acid of 

 the original, (ruin pa <_' wdKOirpoc, Vaccae fimus. — Edit. 



