^^ PROCESS FOR FABRICATING ALUM. 



nre ignited, x^'hlcli. a reverberatory furnace is filled, and wherein a brifk 



cooled, pounded, fi^e is kept up for two hours, or until the infide of the furnace 



and one fourth ... *^, "^ , _, , . . , . /- . « i , i 



of fulphuricacidis oblcurely red. The calcinatidn being nmlned, the clay is 



water is added reduced to powder and put into a found calk ; one. fourth of 

 times^thc acid. *^^ vveight of fulphuric acid is then poured over it, at fcveral 

 intervals, agitating it Urongly upon each addition. As foon 

 as the diflengaged vapours of muriatic acid are diflipated, 

 a quantity of water equal to that of the acid is added, and it 

 ^ is ftirred as before. This produces a combination betweeh 



the acid, the earth, and the water, fo rapid, that the mixture 

 heats, fwells and emits abundance of vapours. Laftly, when 

 the heat has abated a little, water is continually added until 

 the quantity amounts to about eight or ten times that of the 

 acid. 

 To the clear When that part of the earth which is ufelefs in the formation 



potalh Is added"^ °^ ^^^ ^^""^ ^^ depofited, and the liquor become clear, it is 

 drawn off into veflels or boilers of lead. A quantity of water 

 equal to that of the liquor drawn off, is then poured over the 

 refiduuni, and afterwards added to the firit : laflly, a folution 

 of potadi is mixed with the lye, in which the alcali amounts 

 to one fourth of the weight of the acid employed, and it is 

 agitated. If the preference be given to employ fulphate of 

 potafh, the quantity ufedmufl be double that of the alcali. 

 Thealuna cryf- After a certain time, the liquor by cooling, affords cryfiak 

 taizeb ycoo- ^^ alum, the quantity of which, when the cryfl:allization is 

 completed, amounts to three times the weight of the acid 

 made ufe of. This alum is refined by diffolving it in the 

 fmalleft pofTible quantity of boiling water; and it is then a* 

 pure as the beft alum of commerce. 

 Thewafhings As therefidue ftill retains fome faline parts. Citizen Curau- 

 f"bf ^u^ent** * ^^" recommends walhing it a third time with a quantity of 

 operation, water fufficient to extra6l all. the fait, and to ufe this inftead of 



fimple water in a fecond operation; by which means, there 

 will not be any lofs. 

 The mother- Thus, without the aiTifiance of heat, the greateft part of 



watersueu the alum formed in the operation is obtained, which is highly 



in making ^ r r i i 



pruffian blue, beneficial. The author recommends the ufe of the mother- 

 waters, which (till contain alum with fulphate of iron very 

 much oxided, in the fabrication of pruffian blue, to which 

 purpofe they are well adapted* 



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