^66 Mr. Henry's Confideratiom on different Materials^ 



3dly, Another clafs confifts of principles io 

 prevalently refinous, that we are obliged to 

 promote their folution in water, by fermentation 

 or by the addition of fome fubftance, which 

 may aft on the rezinous particles. For this 

 purpofe alkaline faks or quicklime are employ- 

 ed ; and by their means we extra6b the colouring 

 matter of fome bodies, fuch as indigo, archil, 

 fafflower and arnarto. Thefe alfo attach them- 

 felves to the cloth, without the intervention of 

 an earthy medium. 



But, the degree of fixity is various in the 

 different articles of the materia tinEloria be- 

 longing to all thefe divifions. Some of them 

 belong to the lefler or falfe dye, as it is called, 

 and are liable to be injured, and even deftroyedy 

 by the action of the fun's rays, air, water, and 

 alkaline or acid liquors. The ingredients of 

 the good dye, on the contrary, in a great mea-- 

 fure withftand the influence of thefe agents-. 



appellation of the aftringent principle, which greatly con- 

 tributes to their fixity, and has much efredt in feparating 

 the earthy parts of the fait employed to afford the above- 

 mentioned bafis. Under this defcripdon are compre- 

 hended, cochineal, madder, weld, quercetron bark and 

 feveral other drugs. But other articles of this divifion 

 feem to be either deficient in this principle, or elfe to 

 poffefs it of fo volatile a nature, that it readily efcapcs, 

 and carries, along with it, the colouring matter, to which 

 it has a clofe attachment. Of the nature of this principle, 

 we ftall hereafter give a more particular detaii. 



Th© 



