34 ACETATE OF ALUMINE PRECIPITATED BY HEAT. 



being then filtered, and exposed to u somewhat hi^^her 

 temperature, a precipitate was formed again. On cooling 

 it did not resume its tninsparencj- immediately below the 

 point at which it lost it ; it was only at a much lower 

 temperature, that the aluminev as wholly dissolved. This 

 isowlnf^ to the coherence the earth has acquired ; and it is 

 observable, that, the longer the heat has been continued, 

 or the higher it has been raised, the more difficultly the 

 aluraine redissolves. 



Another acetate of aluinine, mucli more concentrated 

 tlian the pvecedin^^, and vvliich was very acid, because a con- 

 siderable sediment had formed in it, became likewise turbid 

 by heat, but a little slower ; and this equally resumed its 

 transparency on cooling-. 

 Nearly half as To determine the quantity of alumitie precipitated from 

 down' byvtea't ^^^ acetate by heat, and wlilch varies according to the 

 as by ami temperature, I took two equal portions of acetate of 



"*''"'''' alumine obtained by the mixture of two solutions of alum 



and acetate of lead made without heat. One of these 

 portions was heated to ebullition, and immediately filtered: 

 the other was precipitated by ammonia. Both precipitates 

 having been washed and dried, the « eight of the first 

 was found equal to nearly half of the second. 

 This of import- These observations may be of great importance to calico- 

 aiice to calico, pvinters ; for, to obtain mordants highly concentrated, 

 they employ hot solutions of alum and acetate of lead. 

 Much alumine therefore must be piecipitated ; and, if 

 the mixture be filtered immediately, tlurewillbea consi- 

 derable loss. To avoid this, it should be suffered to cool 

 completely, before it is filtered, or decanted off; and 

 frequently stirred, that the alumine may redissolve. With- 

 out these precautions the acetate of aluraine would be very 

 acid; and this no doubt is the reason, why it is usual to 

 Methods of add chalk, to it. It is easy however, to prevent the decom- 

 preTenuagit. J.,^si^^oil of the acetate uf alumine by heat. The addition 

 of aUiin, wiiich,' as is well known, has the property of dis- 

 solving alumine, will for this reason prevent the acetate 

 from becoming turbid. A great excess of acid would ao- 

 bwer the same purpose as alum. "=' 



From the preceding observations too we fhy easily con- 

 ceive 



