Of assays by the dry way

—The a ay by the dry way has for its object, to show the nature and proportion of the metals contained in a mineral substance. To make a good a ay, however, it is indispensably nece ary to know what is the metal a ociated with it, and even within certain limits, the quantity of the foreign bodies. Only one metal is commonly looked after; unle in the case of certain argentiferous ores. The mineralogical examination of the substances under treatment, is most commonly sufficient to afford data in these respects; but the a ays may always be varied with different views, before stopping at a definite result; and in every instance, only such a ays can be confided in, as have been verified by a double operation. This mode of a aying requires only a little experience, with a simple apparatus; and is of such a nature as to be practised currently in the smelting works. The air furnace and crucibles employed are described in all good elementary chemical books. These a ays are usually performed with the addition of a flux to the ore, or some agent for separating the earthy from the metallic substances; and they po e a peculiar advantage relative to the smelting operations, because they offer many analogies between results on the great scale and experiments on the small. This may even enable us often to deduce, from the manner in which the a ay has succeeded with a certain flux, and at a certain degree of heat, valuable indications as to the treatment of the ore in the great way. See Furnace . In the smelting houses which purchase the ore, as in Germany, it is nece ary to bestow much attention upon the a ays, because they serve to regulate the quality and the price of the schlichs to be delivered. These a ays are not by any means free from difficulties, especially when ores containing several useful metals are treated, and which are to be dosed or proportioned; ores, for example, including a notable quantity of lead, copper, and silver, mixed together. In the central works of the Hartz, as well as in those of Saxony, the schlichs as delivered are subjected to docimastic a ays, which are verified three times, and by three different persons, one of whom is engaged for the interests of the mining partners, another for that of the smelting house, and a third as arbiter in case of a difference. If the first two results of a aying differ by 1 ⁄ 2 loth (or 1 ⁄ 4 ounce) of silver per cwt. of schlich , the operations must be resumed; but this rarely happens. When out of the three a ays, the one differs from the two others by no more than 1 ⁄ 4 loth of silver per cwt., but by more in one, and by le in another, the mean result is adopted. As to the contents of the schlich in lead, the mean results of the a ays must be taken. The differences allowed, are three pounds for the schlich , when it contains from 12 to 30 per cent. of lead, increasing to six pounds for schlich , when it contains le than 55 per cent. of that metal. A aying forms in great establishments, an important object in reference to time and expense. Thus, in the single work of Franckenscharn, in the Hartz, no le than 300 a ays have to be made in a threefold way, every Monday, without taking into account the several a ays of the smelting products which take place every Thursday. Formerly fluxes more or le compound were employed for these purposes, and every a ay cost about fifteen pence. At present all these a ays are made more simply, by much cheaper methods, and cost a penny farthing each upon an average.