PROCESS FOR FABRICATING ALUM. ^5 



He confiders the fabrication of alum as particularly ad- This procefs 

 vantageous to the manufadurers of prufliaii blue, becaufe ^^'^j^^^^jj^g^.g^f 

 they may calcine their clay at the fame time with their animal pruffian blue* 

 matters, without any increafe of expence. They will have 

 no need in that cafe to add potafh ; and the prefence of iron, 

 inftead of being injurious, will, on the contrary, be very 

 ufeful. If they are defirous of fabricating alum for fale, they 

 may ufe the folution of fulphate of potafli arifing from the 

 wafliing of their pruffian blue, and which is ufually \oi\, in- 

 fiead of water, to diffolve the combination of alumine and 

 fulphuric acid. The refiduums or refufe of the diftillers of^efuleof the 



r ' II ,. , t . r r ^L diftillation of 



aquafortis are equally applicable to the lame purpoles : they aquafortis m^t 

 contain the alumine and potafti requifite to the compofition of l««f«<i» 

 alum, and it will be fufficient to fprinkle this fubflance, re- 

 duced to powder, with fulphuric acid, and to add the neceffary 

 quantity of water to the mixture, proceeding as has been 

 directed above. The mother-waters of thefe alums are alfo 

 ufeful in the fabrication of pruffian blue. 



We may alfo obferve on this occafion that the refufe of the'' contains aa 

 diftillers of aquafortis contains more alcali than is required for 

 the faturation of the fulphate of alumine formed by the clay, 

 and that to obtain the greateft poffible quantity of this fub- 

 ftance, it is neceflary to add an eighth by weight of this earth 

 calcined, according to the procefs of Citizen Curaudauj and 

 that in ufing about fixty parts of acid to a hundred of this 

 earth, at leaft one hundred and eighty parts of very fine 

 alum are obtained. 



Citizen Curaudau affirms, that he has for a long time pre- Profits from 

 pared alum by thefe different proceffes with an advantage of ^.^^^^P^^^^^^ 

 more than 25 per. cent, over that of commerce, and that, 

 notwithftanding the price to which it has now fallen, he flill 

 derives from 10 to 12 per. cent, profit. Laftly, the manu- 

 facturers of pruffian blue, to whom the potafli would be no 

 expenfe, would at this time gain from 17 to 18 per. cent, by 

 making this fait artificially. 



From the contents of this report, is is feen that the memoit 

 of Citizen Curaudau contains the refults of experiments made 

 on a large fcale, highly interefting to manufacturers and 

 merchants, and that, in this view, it will be ufeful to circulate 

 them through the channel of the fcientific Journals. We are 

 . therefore of opinion, that the clafs will give much credit to 

 Vol. VII.— -Januaky, 1804. F Citizen 



flea 



