Then into a low, darksome shed, where from one end to the other you see nothing but leaden evaporating pans and cisterns, some steaming, and all containing liquor in different states of preparation. That from which the most water has been evaporated—the concentrated solution—has a large cistern to itself, where its tendency to crystallize is assisted by an admixture of liquor containing ammonia in solution, and immediately the alum falls to the bottom in countless crystals. The liquor above them, now become ‘mother liquor,’ or more familiarly ‘mothers,’ is drawn off, the crystals are washed clean in water, are again dissolved, and once more boiled, mixed with gallons of mothers remaining from former boilings. When of the required density, the liquor is run off from the pan to the ‘roching casks’—great butts rather, big as a sugar hogshead, and taller; and in these is left to cool and crystallize after its manner, from eight to ten days, according to the season. The butts are constructed so as to take to pieces easily, and at the right time the hoops are knocked off, the staves removed, and there on the floor stands a great white cask of alum, solid all over, top, bottom, and sides, except in its centre a quantity of liquor which has not crystallized. This having been drawn off by a hole driven through, the mass is then broken to pieces, and is fit for the market; and for the use of dyers, leather-dressers, druggists, tallow-chandlers; for bakers even, and other crafty traders.
Looked at from the outside, there is no beauty in the cask of alum; but as soon as the interior is exposed, then the numberless crystals shooting from every part, glisten again as the light streams in upon them; and you acknowledge that the cunning by which they have been produced from the dull slaty shale is a happy triumph of chemical art—one that will stand a comparison with a recent triumph, the extraction of brilliantly white candles from the great brown peat-bogs of Ireland, or from Rangoon tar. Perhaps some readers will remember the beautiful specimen of alum crystals—an entire half-tun that stood in the nave of the Great Exhibition.
Alum is made near Glasgow from the shale of abandoned coal mines, soaked in water without burning. After the works had been carried on for some years, and the heap of refuse had spread over the neighbourhood to an inconvenient extent, it was found that on burning this waste shale, it would yield a second profitable supply of alum. Moreover, artificial alum is manufactured in considerable quantities from a mixture of clay and sulphuric acid.
In going about the works it was impossible not to be struck by the contrast between the sooty aspect of the roofs, beams, and gangways, and the whiteness of the crystal fringes in the pans, and the snowy patches here and there where the vapour had condensed. And in an outhouse wagon-loads of ‘rough Epsoms’ lay in a great white heap on the black floor. This rough Epsoms, or sulphate of magnesia, is the crystals thrown down by the mother-liquor after a second boiling.
In our goings to and fro, we talked of other things as well as alum; of that other mineral wealth, the ironstone, to which Cleveland owes so important a development of industry within the past fifteen years. The existence of ironstone in the district had long been known; but not till the foreman—jointly with his father—discovered a deposit near Skinningrave, and drew attention to it, was any attempt made to work it. Geologically the deposit is known as clayband ironstone; hence clay will still make known the fame of this corner of Yorkshire, as when the old couplet was current—
“Cleveland in the clay,
Carry in two shoon, bring one away.”
If I liked the foreman at first sight, much more did I like him upon acquaintance. He won my esteem as much by his frank and manly bearing, as by his patient attentions and intelligent explanations; and I shook his hand at parting with a sincere hope of having another talk with him some day.