fannfactuTe of Alum.-The common mode of making sulphak of alumina (alum ) from shale or china clay, is lly mixing the aluminous earth with dilute sul pbmic acid and [Lpplying a gentle heat. The process is tedious. A quicker method of manufacturing alum has IJoen patented by A. A. Croll, of London. It con Hists in reducing the aluminous shale or china clay to powder, heating it to about 3000 Fah., then causing an OC1Wl1 qua.ntity by weight of strong sulphuric acid previously heated to 3000 Fah.,

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... to flow into the ves sel containing the heated shale. The mass is then stirred and allowed to stand until the temperature is reduced to about 150°. The sulphuric acid unites with the alumina in the clay forming alum. The mass is now treated with boiling water which dis solves the sulphate of alumina, and the liquor is then nlll oil into another vessel in which it crystalizcs, [ul'ming the alum of commerce.