The crater of Vulcan°, one of the Lipari group, is the seat of similar volcanic phenomena, by which a large amount of boracic acid vapour is generated. Till within a few years of the present time, the products from this 80111T8 were very crudely gathered, by means of convict labour; but since the property has passed into the hands of a British capitalist, proper appliances have been erected for collecting and concentrating the acid, and utilizing the other substances produced. There is nothing in these constructions which calls for detailed description. England annually imports some few thousand pounds of the crystallized acid from this source.
The great potassic salt-beds of Prussia, Anhalt, and Saxony, representing in all probability the upper deposit of a large lake, and resulting from natural evaporating and crystallizing processes protracted over a space of some thousands of years, are another source of boracic minerals. The borders of this vast deposit are composed of the less eoluble potash salt called kainite, which is a double sulphate of potash and magnesia ; while in the interior, the minera clarnallite, a double chloride of potash and magnesia, is met with. It would seem from this, that the less soluble salts were first deposited, while the more soluble kill remained in solution in the deepest parts of the basin.
The extensive boring operations, successfully undertaken here by the Continental Diamond Bock-boring Company, afford valuable and interesting details of the strata constituting the forma tion. The first bore was put down at the supposed edge of the ancient salt lake. It penetrated New Red. Sandstone (about 680 ft.), then gypsum and anhydrite (97 ft.), to the salt clay layer which is the characteristic overlying stalitum of the potash salts, and generally supposed to have been the means of preserving them from doludation. Next came a 1.tyer of impure coloured salts, forming the transitory covering of the valuable potash salts, and at 835 ft., the pure kainite layer was struck, and sunk through for about 50 ft. In this kainite bed, are found not inconsiderable quantities of bolacito, chiefly in small uests or nodules in the upper part of the bed. It also occurs in nodules in the carnallite.
When in a pure condition, this so-ealled Stassfurtite, or Stassfurt boracite, consists of boracic acid, magnesia, and chloride of magnesium. In its raw state, however, it is usually much conta minated with forei4n salts, sometimes to the extent of 50 per cent. The following analysis is stated, by Dr. Klause, to fairly represent the composition of the raw product as brought to market :— Boracic acid 52.39 per cent. Chloride of soda 1.28 per cent.
Magnesia 23.13 „ Sulphate of magnesia . 0.87 „ Chloride of magnesium .. 12.11 „ Sesquioxide of iron .. 0.71 „ „ potash .. 3.46 „ Water .. 6.02 „ In other words, the percentage of berate of magnesia present is about 85. In order to extract
the boracie acid from the mineral, it is washed and dried, then coarsely ground ; about 237 lb. (105 kilos.) are then placed in a leaden pau, with so much water as to render the mass pasty, but not sufficient to cover it. The pan is built in over a grate, so that it can be heated from below without the fiame coming into actual contact with it, and rests on fire-clay slabs, or (less advisedly) on iron plates. Several pans are placed in a row, and heated by the same fire. The paste is stantly stirred with a wooden spatula, and after one to two hours, the solution' is run out throiigh hole in the bottom of the pan. This opening is fitted inside with a strainer, whose mesh does not exceed 0.01 in., which holds back the powder ; it is closed on the outside with a wooden plug, or, better, hy a leaden valve made air-tight with imliarubber. The first muddy portion of the outflowing liquid is thrown back, to prevent any waste of materials. When the liquid has thoroughly drained off, 20-30 pints of water at a time are passed over the surface of the sediment, and allowed to run rapidly through. The outlet is again closed and the sediment is well mixed with about 66 gallons (300 litres) of water ; after which is added 330 lb. (150 kilos.) of crude hydrochloric acid of 1.16 sp. gr., and the whole is well stirred. The pans are again heated, care being taken that the contents of the first do not reach a temperature above 66° (150° F.). Before solution takes place, an occasional stirring is necessary ; but as soon as it has finished, the fire is withdrawn, the liquor is allowed to settle for a few rninutes, and is then let out, through the opening, into stone or iron crystallizing vessels. The impurities will have been deposited in the pan, and the outflowing liquor should be clear. While the solution is becoming perfectly cool, the pans are cleaned out and refilled. When the boracic acid has crystallized out, which it does at a temperature of 15°-20° (59°-68° F.), or less, the lye is let off; the acid is pressed between cloths, rinsed with a little clean water, again pressed, and dried. Instead of pressing the acid, it may be drained, to free it from the lye. The first and most important crop of boracic acid crystals are thus got quite dean. The lyes are mixed and evaporated as often as any boracie acid crystallizes out. The last small proportion thus extracted, containing 5-10 per cent. of foreign salts, is either placed separately from the clean product and valued accordingly, or is thrown into the next panful of solution. The final lye is allowed to run away, or it may be evaporated down to 45° B. (1.321 sp. gr.) and an irnpure chloride of magnesia be obtained from it. In the latter case, the solution, while still hot, is run into strong vessels, where it will form a solid mass after several hours' rest.