.398 Mr. Henry's Co>2fiderations on different Materials, 



be precipitated by the aftringent colourincr 

 matter. 



For this reafon alfo, in the procefs of callico 

 printing, the earth of alun:i is made to chang_e 

 its natural acid for the acetous. For by this 

 means, not only a fait is prepared, capable of 

 diflblving more copioufly in water than common 

 alum, but, the acetous acid being more loofely 

 attached to the aluminous earth, is, as it be- 

 comes concentrated by drying, eafily driven off 

 by heat; the earth being left fpread upon, an4 

 cemented to, the callico. 



When fpeaking of the ufe of animal fub- 

 ftances, it was obferved, that they yield feveral 

 different acids by various modes of analyfis, viz. 

 The phofphoric, the febaceous, the PrufTian and 

 the faccharine. Of thefe the two firft are formed 

 in the animal fyftem, the third is perhaps the 

 creature of fire, and originates from a combination 

 of fome of the more fimple conftituent parts of 

 animal fubftancesj and of the laft it fhould feem 

 that thefe fubftances only contain the bafis*. 

 M. Bertholet by uniting caullic alkalis with 

 animal fubftances is faid to have found them 

 neutralifed, and that the animal matter, when 

 afterwards feparated from the alkali, is no longer 

 fufceptible of putrefaftion. This animalifed neu- 

 tral fait may be decompofed by means of alum, 



■* Critical Review, vol. LXII. p. 377. 



and 



