Mr. Ckum on the Acetates of Alumina. 299 



ous acid and the potash of the original material, together with a little 

 iron and chloride of sodium. It has the formula 



ALO3, 3SO3+ 18H0 



first observed in 1825 by Boussingault in the hair-like substance found 

 among the black schistus of the Andes of Columbia, near Bogota. He 

 afterwards found the same substance in the volcano of Pasto, (north of 

 Quito,) where it is formed by the action of the sulphurous vapours upon 

 the schistus. It exists there in such quantities as to have enabled the 

 Pastusos to become the manufacturers of chemical products for the whole 

 country. They dissolve the alum in water, evaporate it to dryness, and form 

 it into spherical masses like camphor, which are altogether free from iron. 

 The same substance is formed in this neighbourhood from a schistus 

 containing pyrites, in which case it is mixed or combined with sulphate of 

 iron. 



The quantity of cake-alum now produced annually at New- 

 castle and at Sowerby-bridge, according to statistics 



furnished me by Mr, Wilson of Hurlet, is 1,500 tons. 



And of crystallized alum (chiefly ammoniacal)in England, 13,200 " 

 Do. do. do. in Scotland, 4,200 " 



Total in Great Britain, 18,900 tons. 



It is estimated by Mr. Wilson that about one-fourth of this quantity is 

 consumed by calico printers, and converted more or less completely into 

 acetate of alumina. There is no other example of a substance so im- 

 portant and so extensively employed in the arts, as acetate of alumina, 

 having been so little attended to by chemists. 



Insoluble Acetates of Alumina. 



I. Insoluble Bitiacetate of Alumina, b Hydrate. An acetate of alumina 

 was produced by mixing together strong solutions of tersulphate of 

 alumina (purified as already described) and of acetate of lead. They 

 were poured slowly together into a vessel surrounded -with cold water, 

 and much agitated to reduce the temperature of the mixture. To 

 the filtrate was added sulphide of hydrogen, to precipitate the lead of 

 the sulphate of lead which remained in solution ; and acetate of baryta 

 to throw down its sulphuric acid. 



The strongest solution formed in this way contained about 5 per cent. 

 of alumina, (from about G lbs. acetate of lead in an imperial gallon of the 

 mixture.) 



When such a solution (or one containing oven 4 per cent, of alumina) 

 is set aside and left at rest at a temperature of GO" or 70° Fahr.,'it begins 

 after four or five days (without losing much of its transparency) to deposit 

 upon the vessel a crust, which continues for some time to increase in 



