evipfoyed in the Art of Dyeing . 179 



solutions of alum in boiling water with different propor- 

 tions of pure carbonate of lime. Wc always found the 

 alum was decomposed by the carbonate of linie, and that, 

 if a sufficient quantity wa'i added, there remained no part 

 of the aluminous salt in solution. The mother-waters 

 contained verv acid sulphate of potass, and the sediment 

 was formed of sulphate of lime and acidulate sulphate of 

 alumina and potass ; whence it follows, that the property 

 possessed by connnon wool of forming a precipitate in the 

 alum bath, and rendering the fluid very acid, is in reality 

 owing to the carbonate of lime it contains. The same re- 

 sult was obtained by aluming common wool five or six 

 successive times in the same bath. But in order to arrive 

 at a general solution of this question, it was necessary to 

 ascertain the nature of the precipitates formed in the so- 

 lution of alum, by different alkaline and earthy substances. 

 We took, therefore, alums with base of potass, and with 

 base of ammonia, which we treated with ammonia and 

 carbonate of potass, so as to leave in the solution but a 

 slight excess of alun). The mother-waters evaporated, 

 contained very acid sulphates of ammonia, of potass and 

 ammonia, and of potass, according to the nature of the 

 alum and of the precipitate employed. The sediment, 

 which was acid sulphate of alumina and potass, or am- 

 monia, treated with sulphuric acid, afforded alum and aci- 

 dulated sulphate of alumina; boiled afterwards a great num- 

 ber of times with distilled water, it was converted into 

 alum, sulphate of potass, and pure alumina. There was 

 always a greater quantity of acidulated sulphate of potass 

 than of alum, even in the last washings. 



Solutions of alum, treated at a boiling heat with pure 

 alumina, were converted into a very acid sulphate of potass, 

 and into acidulated sulphate of alumina and potass. These 

 results do not at all correspond with those obtained by 

 M. Vauquclin in his experiments upon the alums of com- 

 merce, for we have never been able to obtain the saturated 

 sulphate of alumina and potass, spoken of by that cele- 

 brafed chemist. 



Thus all the alkaline and earthy substances mixed in 

 suitable proportions with solutions of alum, converted that 

 salt into acidulated sulphate of potass, or ammonia, and 

 into insoluble acid sulphate of alumina and potass or am- 

 monia, for which reason wq. have named it the acidulated 

 sulphate instead of the saturated sulphate, the name it has 

 borne until now. It is evident, that if too great a quantity 

 M 2 of 



