The crude salt obtained from the tar fetches about 20/. per ton. Being impregnated with several volatile matters, it can scarcely be used for the manufacture of ether aneumaiacal prepara tions, and without considerable expense and trouble.
Ae commercial sulphuric acid contains more or less arsenious acid, it is easy to conceive that the continued uee of large quantities of this salt as a fertilizer may become a subject of great interest to the toxicologist.
Aqueous Solution of Ammonia. — Water absorbs Ammonia with avidity. 1 volume of water at 0° dissolves 1050 times its own volume of the gaa, and at 25° 580 times its volume. The Liquor Ammonia Fortiss. of commerce has a specific gravity of 0.880 and consequently contains 38.2 per cent. of ammonia. The absorption by water gives place to a rise of tem perature; consequently in the manufacture of this article it is necessary to surround the vessels in which it is collected with ice; some manufacturers place ice in the condensers themselves, which rapidly takes up the gas and becomes liquid ; on account of this, a small residuum will be found on evaporating a little of the solution to dryness in a platinum dish and igniting. When made in glass vessels it will be found to act slightly on the glass ; earthenware allows the gas to escape though its pores, it is said, and consequently it is made on the large scale by condensing in vessels of iron. Copper or lead are not admissible, as their oxides are dissolved by ammonia. A quantity of sal-ammoniac (this is the salt usually employed, as a soluble salt of lime is formed, which can be easily removed from the retort) is placed in an iron retort, with 14 to 1/ times its weight of slaked lime, and the same quantity of water ; the retort is connected with a aeries of Woulfe's bottles, made of cast iron, which are kept perfectly cool. The apparatus is shown in Fig. 195. A is a two-branch piece leading from the still, so as to connect with two series of bottles. W is a wash-bottle, with outlet 0, so as to draw off the accumulating water ; B B' B" and B"' are bottles containing water or ice ; C, a circulating pipe ; P, a pressure-gauge or safety-tube ; D, an outlet for the ammoniacal solution ; and R, the connection for the still. In the first bottle, W, the
water and the impurities which are mechanically carried over are condensed or arrested. The retort is gradually heated so as to give a slow current of gas and to ensure its absorption. The bottle nearest the retort will become strongly saturated, whilst those in succession will be more or less impregnated with the gas. As soon as the contents of the first bottle are fit for removal, they cau he drawn off and the bottle filled either with fresh water, or the weaker solution from one of the next bottles. Since the solutions are lighter according to their degrees of saturation, Lt convenient method is to connect the bottles together at their lower tubulures, and to make the shorter limb of the leading tubes dip just under the liquid, so that the pressure of the gas will drive the lighter and more highly charged portion over into the next receiver and so on to the end of the series, the heavier portions are then driven towards the retort, which serves to create a circulation of the liquid and gives an equal degree of saturation. The retort may be heated in a water bath or by means of a steam jacket. W and B, &c., are Woulfe'a bottles. W receives the impurities and steam coming from the retort. B B', &c., are Woulfe's bottles in which the absorption takes place. A safety tube P, and outlet for drawing off the liquid should be supplied to each bottle. Lime being liable to great variation, it is necessary to use this article in excess. This method of preparation suggests a means of testing the lime which is convenient and simple. The lime is first sampled as carefully as possible, and a weighed quantity, say 100 grains, is taken and placed in a weighed filter ; a warm solution of sal-ammoniac, rather strong, is poured over the lime and continued as the liquid filters away with any lime in it (which can be determined by means of oxalate of ammonia); the residue on the filter is well-washed, dried and weighed ; the loss indicates the amount of caustic lime present. Good hard atone lime can be obtained which keeps better than the softer kinds, yielding 95 per cent. of caustic lime.