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Some time ago, in an article entitled "How to make Oil of Vitriol," we gave a full description of the processes usually employed in the manufacture of that commercial acid ; and we now propose to carry the reader a step further into one of the numerous applications of this most useful of acids. Carbonate of soda, British alkali, or, as it is most commonly called among the manufacturers, " soda ash," is used as the practical source of alkali, and in a great measure it is also used as a source of carbonic acid. There is scarcely any chemical process which can be carried on without its aid, and it forms (when pure) the most useful re-agent of the laboratory. The price is regulated by the actual percentage of pure soda or oxyd of sodium which it contains, and this is ascertained in an ingenious and simple way. The weight of soda being accurately known which will combine with a definite weight of carbonic acid, or in other words, the equivalent proportions of their composition being well established, and it being equally well known what amount of pure vitriol will combine with the same weight of soda, it is only necessary to make such a i solution of vitriol that one measure of it (this measure is arbitary) will exactly combine with 1 per cent of soda in any compound, and the means for testing the amount of soda is at hand. A quantity of soda ash is taken, say one huhdred grains, and dissolved in warm water; a piece of litmus paper reddened by acid is then placed in the soda ash, and it instantly becomes blue from the alkaline nature of the solution. Then a quantity of standard vitriol is added (that is, vitriol made so that one measure equals one per cent of pure soda) drop by drop, with frequent stirring, until all the carbonic acid is expelled, and the vitriol has taken its place in combining with the soda; the moment all the soda is saturated with the stronger acid, the litmus paper again begins to redden, and the number of measures of acid taken to produce this change gives exactly the amount of soda in the ash. Now to manufacture this soda ash is a somewhat difficult process, because carbonic acid is one of the weakest of acids; and to make it replace the acids (such as muriatic, sulpl;uric, and nitric) which are usually found combined with soda, and at the same time render the processes sufficiently cheap to en-iblesoda ash to be produced in large quantity, was a problem for chemists to solve. It has been solved by the united aid of many chemists ; and it is questionable to whom the honor Df being the father of modern alkali-making belongs. We are inclined to believe that rennant, of Glasgow, deserves the greatest share of credit. Soda occurs in nature most plentifully in ihe form of common salt, or as chemists call it, chloride of sodium; and therefore this is aaturally the foundation of all compounds of soda which are produced as triumphs of the chemist's art. But how to displace this strong icid (hydrochloric or muriatic) by another ? lo do this we must summon to our aid the powers of mighty vitriol. A quantity of common salt, generally about four hundred pounds, is placed in an iron pot, which is so built in the fire-place of a furnace that the flames and heated gases all play over it, and then a quantity of vitriol is added. A workman keeps the whole stirred with an iron ladle or spade, while the fire plays on it for four or five hours, until the whole of the chlorine gas is driven off as muriatic acid, and sulphate of soda remains in the pot, this is called " salt cake." Neither the pots or Ladles last very long, and the iron from them iiids much in the contamination of the salt 3ake, which is scraped out while hot, and in a semi-fluid, or rather, viscid state, on to the ground, where it is allowed to cool. This is then broken up, and mixed with small coal and lime. This mixture is then heated for many hours on the hearth of a reverberatory furnace until the whole has assumed a plastic state, when it is raked out into iron barrows, and the hydro-carbon vapors burst from the heated mass in tongues of yellowish-blue flame—technically called ' candles." This product is "black ash," and contains the carbonate of soda, or soda ash, which has to be extracted from it by water. When sufficient solution is obtained, it is run into a suitable shallow evaporating pan, exposed to a high heat, and as it loses the water the mass is well agitated, to prevent crystallization, and the product is the soda ash of commerce. When crystallized soda is required, the solution of the black ash is placed in vessels, and allowed to evaporate slowly, when the crystals form with t^n equivalents of water combined with them. The refuse, or insoluble portion of the "black ash," has been found to contain many valuable organic compounds ; and we have no doubt that shortly some cheap method will be discovered of making this refuse the fountain of the cyanides—the ferro and ferri-cyanides—and other equally valuable salts, all of which will tend to cheapen the staple, carbonate of soda.