compounds, classed as precious stones, are the ruby, sapphire, garnet, turquoise, lazulite, topaz, etc. The ores from which aluminium is commercially reduced. are bauxite, cryolite, and corundum. The chemical method of producing aluminium has been superseded by the cheaper and more satisfactory electrical process. There are three electrical methods, the first depending on the heating effect of the electric current and producing aluminium alloys only, whereas by the two latter methods aluminium salts are submitted to electrolytic action at a high temperature, pure metal being produced. The sheet-metal worker would do well to thoroughly acquaint himself with the many peculiarities of aluminium, which is replacing other metals for ornamental sheet metal work and in the formation of culinary and other utensils, for which purpose its indifference to the action of most acids and to atmospheric conditions renders it especially suitable. The great disadvantage of aluminium is the difficulty encountered in forming reliable soldered joints. This is caused by the formation of an oxide on the surface of the heated metal, the oxide preventing the soft solder from alloying with the aluminium and producing a good joint. With care the difficulty can be surmounted by employing soldering alloys of an easily fusible nature and by melting them with a special copper bit. Good solders for the purpose are given by authorities as follows: Tin 95 parts, and bismuth 5 parts. Tin 97, bismuth 3. Aluminum 2.5, zinc 25.25, phosphorus 25, tin 72. Aluminum 10, tin 90. Cadmium 50, zine 20, tin 30. The copper bit should be wedge-shape and bent roundly to a quarter circle, its edge is then at right angles to the aluminium, and by lightly moving the

bit backward and forward over the metal and the flowing solder the film of oxide can be removed. The coated surface can then be soldered with an ordinary copper bit.

Antimony. This is a bluish white metal, very crystalline and brittle, and so can easily be powdered. Its chief use is in the formation of serviceable alloys, such as white metal and pewter, to which it imparts brittleness. The melted metal rapidly oxidizes if exposed to the air, and if highly heated burns with a white flame, giving off fumes of antimony trioxide. Antimony is dissolved by hot hydrochloric acid, hot concentrated sulphuric acid, and aqua regis, and if treated with nitric acid forms a straw-colored powder known as antimonic acid. Commercial antimony contains impurities in the form of potassium, copper, iron, and lead. Antimony occurs native, but generally the metal is found in combination with others, the chief antimony ore is stibnite. The antimony is recovered from this ore by two distinct processes, by the first of these is separated the antimony sulphide, which is in its. turn refined by the second process. In Germany, where much of the commercial antimony comes from, the ore is placed in covered pots having perforated bottoms, below which are receivers. Between the pots is the fire the heat of which fuses the sulphide, which runs through the holes into the receivers. Crucibles heated in circular wind-furnaces are employed to refine the sulphide. The charge is 40 pounds of sulphide and 20 pounds of scrap-iron, and the product is antimony and iron sulphide, which is again melted, this time with sulphate of soda and some slag, a product of the next process. The resultant metal is melted with pearlash

and slag, and cast into ingots. Antimony can also be produced by electro-deposition.

Bismuth. This metal is reddish white in color, and has a bright lustre. It is very brittle and crystalline, volatilizes at a high temperature, and, burning, forms a crystalline scale flowers of bismuth. The most important use of bismuth is in forming alloys, as its addition to any metal has the effect of considerably lowering the melting-point of that metal. Bismuth may be alloyed with antimony, lead, or tin. Bismuth solders. may be formed of: Tin 4 parts, lead 4 parts, bismuth 1 part. Tin 3, lead 3, bismuth 1. Tin 2, lead 2, bismuth 1. Equal parts of tin, lead, and bismuth. Tin 2, lead 1, bismuth 2. Tin 3, lead 5, bismuth 3. Bismuth is found in the metallic state in the form of bismuthglance (bismuth and sulphur), in combination with oxygen as an ochre, and in the ores of silver, lead, tin, copper, and cobalt. Furnaces for reducing bismuth each contain a number of inclined iron tubes, in which the ore is placed. A wood-fire is lighted, and the fused bismuth, together with some impurities, flows through apertures at the lower ends of the tubes into clay or iron pots heated by a fire underneath. The sulphur and arsenic contained in it are removed by again fusing the metal, this time accompanied by one tenth its weight of nitre.

Gold. This metal has a very limited application in the art of the sheet metal worker, but merely on account of its comparative scarcity to other metals, and hence its expensiveness. Were it not for this, its high malleability and ductility would cause it to be very extensively used in many of the industrial arts. So malleable is gold that it may be reduced to leaves only

the 290,000th part of an inch in thickness. It is but very slightly affected by the atmosphere, and resists the action of all solvents with the exception of selenic, aqua regia, and aqueous chlorine. Gold is found in a metallic state in the form of grains in sand and it is then often in combination with silver, copper, platinum, or iron. Veins of gold quartz occur, and occasionally the metal is found native in lumps, termed nuggets. The ores of galena, copper pyrites, and iron, sometimes contain traces of gold.

Tin. This metal has nearly the lustrous whiteness of silver, is highly malleable, harder than lead, but is not very tenacious. It oxidizes only on being heated, when it forms stannic oxide. Tin can be decomposed by many acids, and, as has already been shown, easily alloys with most metals. Tin-plate as used by the sheetmetal worker is not solid tin, but steel-plate thinly coated with tin by a special process. Many of the more important alloys have tin as their principal constituent, some of these alloys are solders. Tin occurs in the form of sulphuret and oxide, but more generally in the form of ore, known as tin-stone. This is smelted either in blast or reverberatory furnaces. In the latter case the treatment is in two stages, one being the actual extraction of the metal and the other the refining. The roasted ore is washed to remove the sulphates, and is then placed in a furnace having an inclined bed and lined with about 8 inches of fireclay. Previous to placing in the furnace, the ore is mixed with anthracite coal and a small quantity of lime and fluor-spar. At the end of five hours more anthracite coal is thrown into the furnace, and in about an hour after that the molten metal can be run off. The re

maining slag is an iron silicate which contains some oxides. To refine the pig-tin, it is placed in a reverberatory furnace and gradually heated to about 450° Fahrenheit, at this temperature the tin melts, and is drawn off into iron pots. The mass left in the furnace contains for the most part iron. On again melting the tin and stirring it with a pole of green wood, it is caused to boil by the escape of gases, and by this means the impurities, such as iron and arsenic, are brought to the surface, from which they are skimmed. Grain tin is made by allowing the molten metal to fall from a height on to a hard cold surface. To produce what is known as common tin, the metal passes at once to the moulds. Refined tin is the result of using better ores and lengthening the poling process. The purest metal in the mould is the upper portion, the middle portion is the common, and the bottom portion is too impure for use at all, and requires another fusing and poling. The ingots are known as block tin.

Iron and Steel. Iron in a state of purity is comparatively little known, the ores of it are various and abundant. In its commercial forms, as plate or sheet, bar, and cast iron, it is well known. As sheet it can be cut into patterns and bent into desired forms, as bar it can be made hot and wrought, that is, shaped by means of the hammer, and when molten it can be run or cast into all sorts of shapes. Cast iron is brittle, crystalline in fracture, and not workable by the hammer. In sheet and bar form, wrought iron is malleable, mostly fibrous in fracture, and capable of being welded. The presence of impurities in bar iron, that is, the presence of substances not wanted in it at the time being, seriously affects its malleability. Thus the presence of