~Cornish Method.~--_Tin Ore Assay._--The ore to be smelted or assayed should be concentrated to say not less than 50 per cent. of metallic tin; though to obtain satisfactory results it should be brought nearer 70 per cent., as with ore containing less than 40 to 50 per cent. of metal there will be a considerable loss both in the assaying and in the smelting. If the ore to be operated on does not contain this quantity of metal, then the sample (if coarse) must be reduced to a fine state, the gangue being removed by vanning, and the ore saved for the fire assay. The method adopted for the determination of tin in the ore is as follows:--About 2-1/2 ounces troy (1200 grains, or about 80 grams) of the ore to be assayed is weighed out and mixed on a flat copper pan (shaped with a long lip) with one-fifth of its weight (240 grains, or 15.5 grams) of powdered culm (anthracite). The mixture of ore and culm is either transferred to a black-lead crucible before the latter is put into the furnace, or, as some prefer, it is carefully swept into a crucible which has been imbedded in the fire. Some assayers cover their pots with a flat cover placed loosely on, while others leave the mixture in the open pot. The furnace, which has been previously fired to a strong heat, is then covered, and the sample is subjected to a sharp fire for a period of from twelve to twenty minutes. No definite time can be stated, as, besides the strength of the fire, the quality and condition of the ore, and the impurities associated with it, greatly affects the time required for the complete reduction of the ore. As soon as the mixture in the crucible has settled down to a uniform white heat, and any very slight ebullition which may have taken place has subsided, the crucible is gently shaken, removed from the fire (the culm-ash or slag which covers the metal being carefully drawn aside with an iron scraper), and the metal is poured quickly into an iron ingot-mould, which is usually placed on a copper pan to save the culm-slag and the adherent metal which comes out with it. The crucible is then carefully scraped, and the scrapings, together with the contents of the mould and pan, are transferred to a mortar. There the ingot of tin is freed from slag and then taken to the scales. The rest, after being finely powdered, is passed through a sieve. The flattened particles of tin which remain on the sieve are weighed with the ingot (the _lump_, as it is called); whilst the siftings are vanned on a shovel, and (the slag being washed off) the fine tin is collected, dried, and weighed with the rest: the whole gives the produce or percentage of metal in the ore. The results of the assays are expressed in cwts. of metal in the ton of ore. The percentage is rarely given and never used in Cornwall. Thus--"13-1/2 Produce" would mean that the assay yielded results at the rate of 13-1/2 cwts. of metal for one ton of the ore. Some assayers use