376 Mr, Henrfs Conftderations en different Materials^ 



from, fuffer to accumulate. Some of the foap, 

 ufed for the •pouringj adheres to the filk, not- 

 withftanding'the wafhing it undergoes j and the 

 alkali of the foap, uniting with the acid of the 

 alum, fome of its earth is precipitated, joins 

 with the detached oil, and forms the incrufting 

 fubftance ; the undecompofed alum and the 

 vitriolated tartar perhaps alfo, in part, entering 

 into the combination*. 



Cotton requires a ftill different treatment — as 

 the vitriolic acid is injurious to cotton, and it is 

 neceffary that the aluminous folutions Ihould be 

 well dried on it, before it be wafhed ; the acid, 

 being concentrated, by the evaporation of the 

 water, would corrode the cotton. It is therefore 

 proper to faturate the fuperabundant acid, previ- 

 ous to the aluming of the cotton ; and for this 

 purpofe 6 or f of pearl afhes is to be added. 



But the aluminous liquor, ufed by the 

 printers, is prepared in a different manner. To 

 three pounds of alum difTolved in a gallon of 

 hot water, a pound and half of fugar of lead is 

 added ; the mixture is ftirrcd together for a 

 confiderable time, and the agitation repeated 

 often, during two or three daysj when a few 

 ounces of whiting are to be added, gradually, 

 as a ftrong effervefcence enfues. On adding the 

 fugar of lead to the alum, a double eledive 

 attra(5lion produces two decompofitions, and two 

 new compounds. The vitriolic acid forfakcs 



the 

 • Macquer, Art de la Teinture de Soie. 



