When three metals have to be united together, they should first be melted in pairs, and afterwards together.

Guettier gives the following suggestions on the subject of fusing the metals :--(l) The melting-pot should be red-hot (a white heat is better), and those metals first placed in it which require the most heat to fuse them. (2) Put the metals in the melting-pot in strict order, following exactly the different fusing-points from the highest degree of temperature required down to the lowest, in regular sequence, and being especially careful to refrain from adding the next metal until those already in the pot are completely melted. (3) When the metals fused together in the crucible require very different temperatures to melt them, a layer of charcoal should be placed upon them, or if there is much tin in the alloy, a layer of sand should be used. (4) The molten mass should be vigorously stirred with a stick, and even while pouring it into another vessel the stirring should not be relaxed. (5) Use a .little old alloy in making new, if there is any on hand. (6) Make sure that the melting-pots are absolutely clean and free from traces of former operations.

Workmen who are unaccustomed to mixing or treating metals while in a liquid state will generally melt such metal upon a blacksmith's forge by applying heat so rapidly that the ladle will become red hot before the metal within it begins to melt. When it has melted, a dross rises to the surface, and is skimmed off by the workmen and thrown away. The skimming process is kept up as long as the ladle remains on the fire. Now, such a course is wrong, because, by applying heat too suddenly, the metals which fuse at lower degrees of heat, sweat out, and are burned before those which melt at higher temperatures become fluid. The dross, as it is commonly called, which rises to the surface, is in many cases the antimony, or hardening property of the alloy, and should not be thrown away. The surface of the melted metal should be kept covered with fine charcoal, which will prevent oxidation. A small lump of sal-ammoniac should also be kept upon the surface of the metal. The metal should always be stirred before pouring, otherwise the heaviest metals will separate and sink to the bottom of the ladle, and a constantly varying quality of metal will be the result.

By melting the metal slowly, and keeping it properly fluxed as described, it will run sharp; each casting will be found uniform throughout, and the metal will be of equal hardness. In observing these simple precautions, much of the dissatisfaction now experienced in using antifriction allocs will disappear.

Nies and Winkelmann have examined the density of metals in a solid and in a liquid state, and find that, contrary to the generally accepted views on the subject, many melted metals expand when they solidify. The results of their experiments are embodied in a paper contributed to the Munich Academy of Sciences. Tin, slowly and carefully heated to its melting-point, floated on melted tin, and rose to its surface even after it had been submerged. By attaching pieces of copper to the floating tin, it was found that the increase of density by melting over solid tin was 0*7 per cent., a difference which is almost as great as that between tin at the freezing and the boiling points of water. Lead and cadmium did not yield as decisive a result. Zinc, however, behaved like tin, but showed only a contraction of 0*2 per cent. In the case of bismuth, the floating test is very easily carried out, as this metal shows as much as 3 per cent. Copper and iron showed a slight difference, the peculiarity in the case of iron being well known, and having been the subject of elaborate investigations by Wrightson.

Alloy Fluxes

The best flux for alloys of copper and tin is rosin. It should be added when the metals are almost melted. Another good flux is sal-ammoniac. In using this flux the copper is usually melted first and the flux added. When it is in the mushy state, after the flux has been put in, the zinc and tin are added. A good flux for old brass is common rosin-soap. It should be added in small lumps, and stirred down into the metal when in the molten state. In forming alloys of different metals, the molten metals should always be kept under a covering of black glass or pulverized charcoal, to prevent oxidation.

Black flux, as it is commonly called, is composed of 7 parts crude tartar, 6 of saltpetre, 2 of common bottle-glass, and by some a small amount of calcined borax is added. These ingredients are first finely pounded and mixed, and then gradually heated in an iron pot or ladle so as to burn them together. Care should be taken not to overheat the mixture, and as soon as it is thoroughly melted and mixed together it should be removed from the fire and allowed to cool. After it has cooled, it is finely pulverized and sifted, and is then ready for use. It has a great affinity for moisture, and should be protected against it by being placed in glass bottles, and the bottles corked up until wanted for use. This is the most powerful flux that can be made. It is but little employed in forming or fluxing alloys, but principally by as-sayers in assaying different kinds of metallic ores. In these assays the quantity of black flux used varies according to the quality of the ores, but the amount is generally about equal proportions of ore and flux. The ore is first roasted, and then finely broken up and mixed with the flux, and the whole is then rapidly heated in a crucible.

If the flux does not make the slag sufficiently fluid to allow the metal to settle, a small amount of calcined borax is added, which makes the slag more liquid, and permits the metal to pass to the bottom of the crucible. The crucible is then removed from the fire, 'and the mixture is either poured from it or allowed to cool in it. After it has cooled, the slag is knocked off with a hammer, and a button of metal is obtained. When using this flux, the clay crucible, without either coal or graphite (plumbago), is preferred, for the flux is very hard on a crucible that contains either of these substances. Black flux is used by some foundry-men in melting the fine scrap sweepings from the floor, and dross and refuse from the crucible. By melting these in a crucible with black flux, they obtain considerable amounts of metal from them that would otherwise be lost. In melting this refuse with black flux, the common clay crucible should always be used. (E. Kirk.)