[353 Mr. Henrfs Conftderations on different Materials, 



little of this volatile alkali, but much acid, 

 liquor. 



It may be added, that vegetable fubftances, 

 whofe oil is wholly deilroyed by nitrous acid, and 

 to whofe texture the mineral acids, in general, 

 are highly injurious, bear fteeping in folutions of 

 cauftic alkali, of fuch ftrength, as would prove 

 totally deftruftive to wool. 



How far thefe varieties, in the component parts 

 of animal and vegetable fubftances, may influence 

 their power of attrafting colouring matter, I do 

 not pretend to determine, but the propriety of a 

 different previous treatment, feems clearly dedu- 

 cible from it. 



Wool has naturally fo ftrong an attraftion for 

 colouring matter as to need but little prepara- 

 tion, previous to the more immediate proceffes 

 of dying ; and it is only neceffary to icour it 

 from a greafy or fatty fubftance, called the yolk, 

 which is contained in the fleece. For this pur- 

 pofe an alkaline liquor is neceflary ; but as 

 alkalis injure the texture of the wool, it is re- 

 quiflte that a very dilute folution be employed ; 

 for were the quantity of lalt greater than is fufR- 

 cient for converting the yolk into a foap, it 

 yrould attack the fubftance of the wool. Putrid 

 urine, therefore, ^is generally ufed, as being 

 cheap, and containing a volatile alkaline fait, 

 which, uniting with the greafy matter, renders it 

 foluble into water.* 



• Hellot Art de la Tcinture des Laines, &c. 



Silk, 



