Mr. John Mitchell, of Calenick, Cornwall, has just specified his patented improvements in purifying tin ores, and separating ores of tin from other minerals. The invention eon-sists in a mode of applying common salt for the purpose of puritying tinwres, and separating ores of tin from otner minerals. The invention consists in a mode of applying common salt lor the purpose of purifying tin ores, and separating therefrom the other metals with which they are usually associated. Before proceeding to operate, and in order to ascertain the proper proportion of salt to be used, the patentee takes O. samples of the tin ore, previously sttfefid and washed, and submits them in mtxrti with different proportions ol salt, (say";l:frs ozs.) to a temperature of about 563 of Darnell's pyrometer, for about three quarters of an hour, using a reverberatory or other turnace. If, on analyzing the oxides thus produced, either sample is found to be pure, then the quantity of salt used ia calcining that sample is a proper proportion to be used. The ores, previously stamped and washed, and salt are mixed together and placed in a reverberatory or other furnace, where they are subjected from three to tour hours to a heat of 163 of Daniell's pyrometer, which should be raised gradually but not exceeded, the object being not to decompose the oxide of tin, but to cause the chlorine of the salt to combine with the other metals presant, so as to render them soluble in water. At the conclusion of the roasting, the ore is thrown into water and washed, after which it is smelted in the usual way. CLAIM.—The mode described of applying common salt for purifying tin ores, and separating ores of tin from other minerals. SULPHATE OF AMMONIA,—Wm. Hunt, of Stoke Prior, patentee.—The object of this invention is to obtain the sulphate of ammonia from the ammoniacal liquor of gas works.— This is effected by making the said liquor to traverse a condenser filled with pebbles and coke, and there brought in contact with sulphurous acid gas obtained by calcining pyrites of any description to drive off the sulphur therefrom. The sulphurous gas may be introduced at the top of the condenser and descend with the falling liquid, or it may be introduced at the bottom ; the gas, however, must be cool before it ia brought in contact with the ammoniacal liquor. The result of the union of the gas with the liquor, is to convert it into a sulphite, by subsequent evaporation and exposure to the air, the sulphate will be produced. This invention should arrest the attention of our gas companies.