as Ohje^s of the Art of Dyingi t^c. 377 



the earth of alum to unite with the calx of lead 

 K& \!ti& Jaccharum Jaturni; and this new fait, 

 poflefTing very little folubility, falls to the 

 bottom of the veffel in form of a white precipi- 

 tate. The earth of aluna, being left at liberty, 

 and in fo minutely divided a ftate,. is attacked, 

 in the act of precipitation, and diflblved by the 

 acetous acid; which, having quitted the lead, 

 is ready to form this new union j and thus a 

 very foluble fait, being the produifl, it remains 

 diflblved in the water; and, when thickened 

 with gum, is applied by means of blocks to the 

 cloth. The piece being afterwards dried in a 

 hot ftove; the vinegar, which as the cloth dries, 

 becomes highly concentrated and very volatile*; 

 not having a ftrong attachment to the aluminous 

 earth, flies off^ and leaves the earth, upon the 

 cloth, ready to receive the colouring matter. 

 And herein confifts the advantage of the change 

 of the vitriolic for the acetous acid. 



Thus we fee that the printer's liquor, for the 

 red and yellow colours, is not, as thofe artifts 

 generally imagine, a mixture of alum and fugar 

 of lead, but merely an acetated argill, or alumi- 

 nous earth, combined with vinegar. The addition 

 of whiting is intended only to neutralife the 



* The vinegar, by its union to the calx of lead, feems to 

 have acquired fome new properties. For on feparating it from 

 the Jead, by diftillation, it always contains fome portion 

 or itner. When the cloth has become dry in the hot flove, 

 Mr. Charles Taylor has obferved flafhes of eleftric light, dart- 

 ing from its furface. 



fuper- 



