424 Mr. J. Wilson's Researches into the Alum Manufacture. 



This process has the effect of peroxidizing the iron, and render- 

 ing the clay more porous. The heat must be regulated carefully, 

 otherwise the clay undergoes a commencement of fusion, in which 

 condition it is nearly insoluble in acid. About 45 per cent, of 

 its weight of sulphuric acid, of specific gravity 1*454, heated by 

 the waste heat of the furnace to about 160° F., is run upon it 

 and digested with it for some months, at the end of which time 

 the mass is lixiviated, concentrated, and the proper quantity of 

 alkali added: the alum precipitates and is purified in the ordi- 

 nary way. 



Concentrated alum or tersulphate of alumina is an article in- 

 troduced of late years into commerce, for which there is a con- 

 siderable demand. The objection to its more general use is, 

 that its composition is not always the same. It is prepared by dis- 

 solving clay in sulphuric acid, and adding ferrocyauide of sodium 

 to precipitate any iron which the acid has dissolved, as prussian 

 blue. The clear liquid is evaporated till it becomes solid on 

 cooling. The prussian blue is boiled with caustic soda to recon- 

 vert it into prussiate of soda, thus avoiding any loss in this 

 respect. 



The two analyses given were made upon a sample of concen- 

 trated alum sent by Messrs. H. Patinson and Co., of Newcastle- 

 on-Tyne. 



The sulphuric acid was precipitated by chloride of barium. 

 25 grains gave — 



I. Sulphate of barytes 27*89 = SO 3 per cent. 38-46 

 II. ... 2761= ... 3808 



25 grains gently heated and then strongly ignited left, — 



I. Alumina . . 4*84= alumina per cent. 19*36 

 II. ... 4*55- ... 18*20 



The sulphuric acid per cent, and alumina being deducted, 

 leave, — 



I. Water per cent 42*18 



II. ... 4372 



or 



100 100 100 



Al 2 3 + 2|S0 3 + 13HO 



2A1 2 3 + 5S0 3 + 26H0? 



