as Ohjetts of the Art ofDyingy (^c. 4P5 



this principle. He found alfo that this matter, 

 (which, if not kept fufpended by fome muci- 

 laginous fubftance, feparares and precipitates 

 from the liquor) refembles, in fome degree 

 martial aethiops, but that it was not, like that 

 powder, attrafted by the magnet, till after it 

 had been expofed to a red heat 5 when it loft 

 its blacknefs, and became of a rufty brown 

 colour: — a proof that the black colour of ink 

 or of the black dye, which is formed on fimilar 

 principles, does not depend, merely, on the 

 iron acquiring phlogifton from the galls. He 

 alfo found that both acids and alkalis deftroy 

 blacknefs thus produced j the former by dif- 

 folving the ferrugineous body, the latter by 

 afting on the allringent principle. He, how- 

 ever, was of opinion, that this principle was of 

 a fixed, not a volatile nature. But our worthy 

 prefident. Dr. Percival, very early fufpedted 

 that this aftringent principle poffeffed fome vola- 

 tility. In fupport of his opinion, he mentions, 

 artichoke .ftalks, lofing their aftringent prin- 

 ciple by being dried in an oven. He likewife 

 appears to be the firft who obferved the aflion 

 of acids and aftringents on each other. 



The fubjed has been farther purfued by the 

 Dijon academicians ; from the refult of whofe 

 experiments it appears, that the aftringent 

 principle is foluble in water, in fpirit of wine, 

 in oils, and in aether j that it rifes copioufly 

 D d 3 in 



