420 Mr, J. Wilson's Researches into the Alum Manufacture. 



tained must have been different from what I examined, as mag* 

 nesia and no lime existed in these liquor3. The liquors are 

 pumped up from the cellars into wooden reservoirs, whence they 

 are allowed to flow into the evaporating boilers. These last are 

 about 60 feet long, 7 feet broad, and from 4 to 5 deep. They 

 are arched over and are made of fire-bricks. At one end is the 

 furnace, and at the other the chimney. The flame and hot air pass 

 over the liquor, and the draught carries off the steam as it rises. 

 During the evaporation, a brownish or buff-coloured substance 

 falls in considerable quantity, which is commonly called a sub- 

 sulphate of alumina; but a specimen which I analysed I found 

 to contain upwards of 50 per cent, sulphuric acid, 25 of peroxide 

 of iron, and about 3 or 4 of alumina. When the liquor has 

 attained the strength 65° to 70° of Twaddel's hydrometer (1 325 

 to 1350 spec, grav.), the boiler is opened and the liquor run 

 into the alum-coolers, which are made of stone. The proper 

 quantity of muriate of potash or sulphate of ammonia is added 

 either in solution or dry; if dry, the mixture is agitated by 

 wooden poles to cause the salt to dissolve and be equally diffused. 

 The coolers are left at rest for about a week, at the end of which 

 time the mother-liquors are made to flow into a tank for the 

 purpose, and the first crystals of alum collected and washed with 

 cold water. These crystals are of a brown colour, being conta- 

 minated by iron, and contain, — 



Sulphuric acid 34-33 



Alumina 6*44 



Peroxide of iron 4" 5 2 



Potash 2-33 



Ammonia 2*81 



Chlorine '36 



Water 49-31 



100 

 The first alum is dissolved in mother-liquor from the second 

 crystallization by means of steam. This operation is performed 

 in a cistern lined with brick about 9 feet deep, to the bottom of 

 which a steam-pipe passes. When the alum has dissolved, the 

 steam is shut off and the deposit allowed to subside. The liquor 

 is run into stone coolers, where the second alum crystallizes. 

 This I found was composed of — 



Sulphuric acid 36-08 



Alumina 960 



Peroxide of iron '88 



Ammonia 3 - 83 



Potash " -73 



Chlorine trace 



Water 48-88 



100 



