tically hydrochloric acid is added to the yellow liquor, sulphurous acid being run in along with the other two streams, keeping the temperature at about 145° Fahr., and proportioning the streams as to yield chloride of calcium and sulphur, which is collected, washed, and dried as before described.

It is of some interest to note that when alloxan (an oxidation product of uric acid) is treated with sulphuretted hydrogen, alloxanthine is formed, and sulphur set free, thus

4C,H,N2O5+2H2S=2C8H10N4010 + S2.

Could the alloxan be regenerated from the alloxanthine, a process might be worked out for the recovery of sulphur in this way. Now, it is well known that alloxanthine may be reconverted into alloxan by moistening it with a mixture of 2 parts fuming nitric acid (1.52 sp. gr.) with one part of ordinary nitric acid (1·42 sp. gr.), when nitrous acid is copiously evolved, and after some time the reaction is complete.

Here, therefore, we have chemical grounds for a process to recover the sulphur from waste, and without any loss of nitric acid, for the nitrous acid evolved could be again converted into nitric acid for further use. The alloxan could be made from guano.

It is worthy of record that among other unsuccessful undertakings for the regeneration of sulphur from waste, is one which originated with Mr. I. Lowthian Bell. He proposed to make factitious pyrites (so called) by heating in a blast-furnace a mixture of soda waste and the residue left by burning pyrites. So far as the mere union of the sulphur and the iron was concerned, the undertaking was

eminently successful, and, in fact, some 2,000 to 3,000 tons of the factitious pyrites were actually made. But, beyond certain destructive influences on the furnaces, the cost was too great at the time to warrant continuation of the manufacture; not only so, but the difficulty was increased by the discovery that the product could only be burnt so as to regain the sulphur for chamber consumption, when in union with coal-brasses or native pyrites. Nevertheless, Mr. Bell has pointed out that should native pyrites experience an improvement in price, or coal a great deterioration, the process might, after all, be employed more or less widely. The least that can be said. of the process is, that it was as ingenious as the undertaking was commendable.

While treating of alkali waste we may conveniently refer to the manufacture of hyposulphite of sodium, although this substance is not largely produced. Its production in Great Britain is, we believe, confined to the Tyne district, and at Walker the process which is followed, is somewhat as now to be stated.

Tank or vat waste is exposed to the atmosphere, whereby the sulphides of calcium are converted into hyposulphite. The product is made into a thin paste or solution with water, and is then heated with sulphate or carbonate of sodium. In this way sulphate or carbonate of calcium is precipitated, while sodic hyposulphite remains in the solution, and is obtained therefrom on concentration and crystallisation.

In 1863 about five tons were made weekly by this method at Walker-on-Tyne. Another process, used at Newcastle, consists in the reduction of sulphate of sodium

to sulphide by means of coal, in a close furnace. The balls' which result from this operation are extracted with water, and the solution after settling, is exposed to a current of sulphurous anhydride. It is then concentrated in the open air, and on cooling the sodic hyposulphite crystallises out.

CHAPTER X.

SODA PROCESSES OTHER THAN LEBLANC'S, INCLUDING THE 'AMMONIA PROCESS.'

UNDER this heading it is our intention to briefly indicate, and in some measure describe, processes which have been proposed from time to time, either as supplementary to, or substitutive of, the one in general use. Most of them are improved modifications of old processes, and have been tried on a limited scale, while others are actually in use to a small extent.

Some years ago Mr. Hunt proposed a process, founded on some experiments of Mr. Gossage, and which, indeed, was an old friend in a new garb. It was proposed to obtain crude sulphide of sodium by fluxing salt-cake with coke or coal; the product was to be broken into lumps and placed in iron cisterns provided with false bottoms, under which carbonic anhydride was forced, the gases passing out at the top. Each vessel was to be heated by steam, and the carbonate of sodium so obtained to be purified by recrystallisation. As for the sulphuretted hydrogen evolved in the reaction, this was mixed with air and burnt under a stratum of oxide of iron kept red-hot by the burning gases, and in this way sulphurous anhydride was produced for use in the chambers. The chief difficulties encountered in the working of such a process are those which Mr. Weldon hopes to avoid,

and as we have already described his process and its advantages in our last chapter, we may pass from its consideration.

Mr. Arrot, Mr. Hunt, and others have also proposed at various times to manufacture caustic soda from the sulphide made as above, by the use of oxides, such, for instance, as those of iron, manganese, zinc, and copper. Where iron is used, a double compound of sulphide of iron and sodium results, which is difficult to manipulate. But in any case a greater difficulty so far, consists in the manufacture of the sodic sulphide. This has been attempted by causing a fused stream of sulphate of sodium to flow through red-hot coke or coal, but with partial success. If by Weldon's plan, good results should be obtained, then these various other processes would merit reconsideration.

The processes we shall next describe, refer to the extraction of soda contained in felspar, cryolite, and other minerals.

Ward proposed to frit any natural silicate, as pumicestone, with calcium fluoride and chalk, in a reverberatory furnace, by which operation, supplemented by lixiviation of the product, a solution of caustic soda is obtained; the residuum he employed as a hydraulic cement.

Newton patented the use of the following proportions:-100 parts felspar, 50 parts phosphate of lime, and 300 to 400 parts of lime, all in powder. This mixture was calcined at a low red heat for two hours, by which means there are formed silicate of lime and phosphate of sodium; the silicate of lime combines with the silicate of alumina, and on lixiviation, the lime decomposes the phosphate of sodium, reproducing phosphate of lime and