weight of the pure acid to be less valuable than as much crude acid as contains an equal quantity of the pure acid, in consequence of the large proportion of sulphate of ammonia contained in the crude acid (sometimes fourteen per cent.), which may be made available in the manufacture of ammoniacal salts. With this view, the crude acid is first washed with cold water (whereby it loses from five to twenty per cent. of its weight), and the washings are concentrated by evaporation, on which they afford a large quantity of a well crystallized salt, which is the double sulphate of magnesia and ammonia. Very little boracic acid is mixed with these crystals; but the motherliquor is a strong solution of boracic acid, which does not afford crystals, though its density is very high.

The process for making borax from the crude acid, as carried on successfully in M. Payen's works at Paris, is the following:* it differs slightly in its details from the method pursued in this country.

The materials operated on are one thousand kilogrammes of the crude acid, twelve hundred kilogrammes of crystallized carbonate of soda, or the equivalent quantity of dry carbonate, or of the sodaash of commerce, and about two thousand kilogrammes of water, minus the quantity which may be furnished by the mother-liquor of a preceding operation and that introduced by the condensation

* Information derived from a paper on the subject, by M. Payen, in the Ann. de Ch. et de Ph. t. ii., 1841, p. 322.

† At an extensive borax work in this country, the proportions of soda and acid which are employed, are, eight parts of unwashed acid, and ten parts of soda-crystals, or the equivalent quantity in soda-ash.

The regular addition of the mother-liquor of one operation to the

of the steam applied as a source of heat. The carbonate of soda is first dissolved in a vat a, fig. 32, lined with lead and heated by steam from the boiler b. The pipe which conveys the steam leads nearly to the bottom of the vat, where it is bent into a horizontal circle and pierced with holes to emit the steam. When the carbonate is dissolved and the temperature of the solution raised to near 212°, the boracic acid is added in quantities of from four to five kilogrammes at a time through the pipe c, and the carbonic acid and other gases then evolved are conducted by the tube d, attached to the cover of the vat, into a condenser e, containing sulphuric acid. The object of passing the gas into sulphuric acid is to collect some ammonia which is disengaged

solution of borax made in the next, is by no means advisable, as the quantity of impurities must then be continually on the increase. The extraction of the whole of the borax from the mother-liquors requires a tedious and somewhat complicated process.

in the state of carbonate. When all the boracic acid has been introduced, the solution ought to have the specific gravity 1.17 (21° of Baumé's hydrometer). Its boiling point is then about 221° Fahr. (105° Cent.).

The supply of steam is now cut off, the opening, c, covered, and the solution allowed to stand for ten or twelve hours. A deposit takes place, and the clear supernatant liquid is withdrawn by the stopcock f, and conducted into crystallizing pans g g.

These vessels are made of wood lined with thick sheet-lead. Their depth is about fifty centimetres (very near twenty inches).

When the crystallization is complete, the mother-liquors are conducted into the cast-iron trough h, placed below the evaporating pans: ii are wooden plugs encased in lead to be withdrawn for that purpose. The impure crystals of borax are detached from the pans, and set to drain on an inclined plane k, the floor of which is of lead: the drainings are collected in the gutter 1.*

After the liquid in the vat a is decanted, the deposit is withdrawn by the pipe m, and received into the cast-iron trough n.

The object of the refining processes to which the crude borax is next subjected is not only the purification of the salt, but the formation of large and hard crystals. The small soft crystals which are procured from a solution of borax on the small scale

* These drainings, and the liquor collected in h, contain a quantity of carbonate and sulphate of soda, together with a little borax; by evaporating the liquid and calcining the residue with chalk and coal, the sulphate becomes converted into carbonate, but the greater part of the borax remains without alteration.

would hardly meet with a purchaser. Such were the crystals obtained in the first attempts to procure borax from the native acid for commercial purposes; but, though quite pure, their appearance formed a serious obstacle to their sale, as it was generally believed that the smallness of the crystals arose from the presence of impurities.

To procure crystals fit for the market, M. Payen proceeds in the following manner. The construction of the necessary apparatus may be understood with the assistance of the annexed cut: a is the vat in

which the borax is redissolved; it is lined with lead, and is of sufficient capacity to contain a solution of nine thousand kilogrammes (nearly nine tons) of borax. The solution is effected with the assistance of heat derived from steam introduced by the leaden pipe b to the bottom of the vat.

The crude borax, and the small crystals of previous refinings, are placed in a basket made of iron rods c, suspended over the vat by a chain and pulleys. The vat being nearly filled with water, the basket is lowered so as to bring it immediately under the surface of the water; the borax is thus dissolved, and the sinking of the dense liquid to the bottom establishes currents in the liquid, which facilitate the solution of the remainder, and render any other agitation unne

cessary.

For each quintal (1cwt. 3qrs. 25lbs.) of borax, about eight kilogrammes (between seventeen and eighteen pounds) of crystallized carbonate of soda are added to the vat, and the solution is brought to the specific gravity of 1.17 (21° Baumé). It is then transferred while boiling to the crystallizing vessel d, which together with its cover is lined with lead. Proper precautions must be adopted to preserve the crystallizing vat in a tranquil state, and to prevent a rapid reduction of its temperature. With the latter object it is surmounted with a double ceiling e e, the space between which and the vat is filled with charcoal powder, the top of the vat being covered with two or three pieces of thick woollen cloth. Underneath the vat is a pavement of flagstones, or smooth bricks, having a gutter which leads into a small reservoir f. This serves to collect any droppings from defects in the soldering of the

vat.

From twenty-five to thirty days, according to the external temperature, are required to complete the crystallization. Its progress may be ascertained by the temperature of the liquid. When between 77°