Of far greater importance are the " manganese tin and zinc bronzes," which were perhaps among the first upon which experiments were made on a large scale. They were obtained by adding to an alloy of copper, tin, and zinc, a certain quantity of " manganese copper," viz., the combination of 70 copper with 30 manganese as above described, by which an increase of at least 9 per cent of strength is obtained over the ordinary alloy. This seems to be greatly due, as in the case of the refined tough copper, to a chemical action of the manganese; for all ordinary bronzes contain more or less of copper and tin oxides, which are reduced to metal by the action of the manganese. An addition of manganese seems, however, to have also physically a strengthening effect, and an addition of 3 to 6 per cent. of manganese copper has been experimentally found to suit the purpose best.

Manganese and tin combine as readily as manganese and copper; tin, however, shows, as in ordinary bronzss, a tendency to separate itself in the middle of thick castings from the other alloys, because it remains longest in a fluid condition, and under the process of solidification it seems to get squeezed out of those parts of a casting which retain the heat longest.

An important series of experiments made at Isabelle-Hutte have shown that the strongest "manganese tin bronze" is obtained by alloying 85 copper with 6 tin, 5 zinc, and 5 manganese copper, so that the cooled product retains something above 1 per cent. manganese. The best mode of procedure is first to melt the copper in a crucible, then to add successively tin and zinc, but manganese copper only at the last moment, when the metals are well stirred up with a rod made from gas retort graphite; a reaction upon the oxides of the metallic bath is clearly noticed, as it begins to boil and to emit sparks after the addition of manganese, of which a portion is carried into the slag. Subjoined is a table of trials made with a series of rough ingots of the metal:-

The absolute strength of these alloys is considerably enhanced when the ingots are subjected to judicious forging or rolling. The White Brass Go. of London, indeed, reaches in this manner with manganese bronze the strength of good steel plates, giving a breaking strain of 27 to 30 tons per sq. in.

Delatot's white metal is composed of 80 parts red copper, 2 manganese oxide, 18 zinc, 1 lime phosphate, fused together. To the melted copper is added the manganese in very small instalments; when this is dissolved, the lime phosphate is similarly introduced, and after the reduction has lasted 1/2 hour, the scum is removed from the surface of the bath, and the zinc is added about 10 minutes before running out. This alloy is said to equal gun-metal in tenacity and resistance, excel it in obviating friction, and cost much less. The fusion of the manganese oxide may be hastened by using a flux composed of 2 parts charcoal, 1 calcium fluoride, 1 sodium borate.