ALUM 117 



feet high, three feet wide at the top, and somewhat -wider at the bottom ; they are 

 made of very strong staves, nicely fitted to each other, and held together by strong 

 iron hoops, which are driven on pro tcmpore, so that they may be easily knocked off 

 again, in order to take the staves asunder. The concentrated solution, during its 

 slow cooling in these close vessels, forms large regular crystals, which hang down 

 from the top, and project from the sides, while a thick layer or cake lines the whole 

 interior of the cask. At the end of eight or ten days, more or less according to the 

 weather, the hoops and staves are removed, when a cask of apparently solid alum is 

 disclosed to view. The workman now pierces this mass with a pickaxe at the side 

 near the bottom, and allows the mother-water of the interior to run off on the sloping 

 stone floor into a proper cistern, whence it is taken and added to another quantity of 

 washed powder to be crystallised with it. The alum is next broken into lumps, 

 exposed in a proper place to dry, and is then put into the finished bing for market. 

 There is sometimes a little insoluble basic alum (sub-sulphate) left at the bottom of 

 the cask. This, being mixed with the former mother-liquors, gets sulphuric acid 

 from them ; or, being mixed with a little sulphuric acid, it is equally converted into 

 alum. 



Alum Liquors, In the alum works on the Yorkshire coast, eight different liquors 

 are met with : 



1st. ' Eaw Liquor.' The calcined alum-shale is steeped in water till the liquor 

 has acquired a specific gravity of 9 or 10 pennyweights, according to the lan- 

 guage of the alum-maker. 



2nd. ' Clarified Liquor.' The raw liquor is brought to the boiling point in lead 

 pans, and suffered to stand in a cistern till it has cleared ; it is then called 

 clarified liquor. Its gravity is raised to 10 or 11 pennyweights. 

 3rd. ' Concentrated Liquor.' Clarified liquor is boiled down to about 20 penny- 

 weights. This is kept merely as a test of the comparative value of the potash 

 salts used by the alum-maker. 



4th. 'Alum Mother-Liquor.' The alum pans are fed with clarified liquor, 

 which is boiled down to about 25 or 30 pennyweights, when a proper quantity 

 of potash salt in solution is mixed with, it, and the whole run into coolers 

 to crystallise. The liquor pumped from these rough crystals is called ' alum 

 mothers.' 



5th. 'Salts Mothers.' The alum mothers are boiled down to a crystallising 

 point, and afford a crop of 'Rough Epsom," which is a sulphate of magnesia 

 and protoxide of iron. 



6th and 7th. 'Alum Washings.' The rough crystals of alum (No. 4) are 

 washed twice in water, the first washing being about 4 pennyweights, the 

 second about 2, the difference in gravity being due to mother-liquor clinging 

 to the crystals. 



8th. ' Tun Liquor.' The washed crystals are now dissolved in boiling water, 

 and run into the ' roching tuns ' (wood vessels lined with lead) to crystallise. 

 The mother-liquor of the ' roch alum ' is called ' tun liquor : ' it is, of course, 

 not quite so pure as a solution of roch alum in water. 



The alum-maker's specific-gravity bottle holds 80 pennyweights of water, and by 

 10 pennyweights he means 10 more than water, or 90. 



The numbers on Twaddle's hydrometer, divided by 2 '5, give alum-makers' penny- 

 weights. 



The alum-maker tests his samples of potash salts comparatively by dissolving equal 

 weights of the different samples in equal measures of alum liquor at 20 pennyweights, 

 heated up to the boiling-point, and weighing the quantity of alum crystals produced 

 on cooling. 



For the above information we are indebted to Mr. Maurice Scanlan, who super- 

 intended for some time the Mulgrave Alum Works. 



: According to him 6 tons of the alum rock at the Mulgrave Works, to the north 

 t of Whitby, yield, after calcination, &c., one ton of alum. 



The true value of the Whitby alums consists in the amount of soluble alumina 

 which they contain, and for calico-printing also in their freedom from iron. 



. The alum-shales not being very generally found over the country, and nature 

 having interposed certain limits to the amount manufactured and the speed of the 

 process, many attempts have been made to obtain alum and sulphate of alumina from 

 other sources. 



A number of these processes will be afterwards described in chronological order, 

 but the following are those only which are at present largely applied in this 

 country. One of the great advantages of the modern processes is the rapidity with 

 which the alum can be manufactured ; thus, an order can now bo executed in three 



