as it gives sharpness to the metal and prevents fouling of the tools. The presence of a little tin is an advantage when hardness is requisite, as in the case of bushes, for example. A little iron hardens brass, and tends to increase its tenacity and elasticity. But it is not advisable to introduce metals other than copper and zinc, unless for specific purposes, as mentioned above. It should be borne in mind that however beneficial the addition of lead, tin, or iron may be in special cases, the simultaneous presence of two or all of these metals is generally injurious, whatever the action of one of them may be when present alone in the brass. In fact, it may be stated as a general rule, not without exceptions, that an alloy of two metals is more stable than that of three or more; and the greater the number of metals alloyed together, the greater will be the difficulty in obtaining uniform and sound castings. Lead especially has a tendency to separate out from the mixture in cooling, producing unsightly black spots, especially when present to the extent of 2 or more per cent.

When the metal is cast in a large mass, or the castings are of considerable size, there may be, as the metal solidifies, a greater proportion of copper in the under portion than in the upper part of the casting, and the alloy is thus liable to be deeper in colour below than above. The constituents of an alloy of two or more metals tend to separate according to their respective densities, and the more numerous the constituents, and the greater the difference of their specific gravities, the more marked will this tendency be; but when the metals are in chemical combination with each other, no such separation will take place.

TABLE OF DIFFERENT QUALITIES OF ORDINARY CAST-BRASS AS DETERMINED BY ANALYSIS OF COMMERCIAL SAMPLES

Brass employed for the production of fine castings requires to possess other properties than those of being able to be filed and turned in the lathe. It must be thinly liquid when melted, and not in any degree pasty, so that it will readily flow into the minutest and most intricate crevices of the mould, and the texture must be fine-grained and uniform throughout. Moreover, as such castings specially require to be sound and free from pinholes, it must be capable of remaining thinly liquid until near the point at which it solidifies, so that the metal may be poured at the lowest possible temperature, thus enabling air and other gases, absorbed during the melting, to escape as much as possible before pouring. When the castings have to be subsequently gilded, it has been found that when the metal is similar in colour to gold, it requires less gold to produce the desired effect than when the brass is of a pale yellow colour. For this reason brass of reddish-yellow colour is preferred. The French have brought the casting of fine articles, as well as larger articles, to a high degree of perfection; clock-cases, statuettes, and other artistic ornamental

ork, are manufactured by them on an extensive scale. loys used for these purposes are often called bronze, but ey are generally brass, with the addition of a little lead d tin, which impart to the metal a bronze-like colour. he following are the proportions used for a few of the rench mixtures:

These alloys are distinguished by a beautiful gold colour, ich very closely resembles that of gold alloys. They are ry ductile and tenacious, can readily be stamped and lled, and admit of a fine polish. According to an old cipe, orëide is prepared in the following manner: "Melt 10 parts of copper and add, with constant stirring, 6 parts magnesia, 3-6 parts of sal-ammoniac, 1-8 parts of lime, and parts of crude tartar. Stir again thoroughly, and then d 17 parts of granulated zinc, and after mixing it with e copper by vigorous stirring, keep the alloy liquid for e hour. Then remove the cover of dross, and pour out e alloy."

§ 31. Talmi or Talmi Gold.-Also termed Abyssinian

gold

Talmi gold is the name given by the French, who use the foregoing alloys for cheap jewellery, which is distinguished by good workmanship, great durability, and a beautiful golden colour. The colour is retained for a considerable time, as it possesses a thin coating of gold, firmly welded to the alloy by rolling, and when the gold is of sufficient thickness the characteristic appearance may be retained for years without alteration. But many cheap imitations are manufactured and sold under this name, which consist of common brass, gilded with a thin coating of gold.

$ 32. Tournay's Alloy is also used in the manufacture of cheap jewellery, as well as for buttons and so-called bronze ornaments. It is composed of 82.5 parts of copper and 17.5 parts of zinc.

$33. Mannheim Gold, Similor, Prince's Metal.—The composition of this alloy varies considerably, as will be seen from the following analysis of three samples :

The first has a yellowish-red tint, and the second one a deeper red. Similor has been much used for buttons and other stamped work requiring a reddish cast of colour.

$34. Tombac.-As stated on a previous page, tombac is a name applied to alloys which by some manufacturers are termed prince's metal, similor, and Mannheim gold. The name is used for alloys so widely different in composition and properties as to lose any significance it may have

formerly possessed, and strikingly illustrates the great need of adopting Dr. Percy's proposition, that the different alloys of copper and zinc should be designated by their percentage composition. The following table will show the proportions of different mixtures.

§ 35. Gilding Metal.-Alloys of copper and zinc containing upwards of 80 per cent of copper have a reddish-yellow or red tint, and are used as a base for gilding. The more nearly the colour approaches to that of standard gold, the more highly is it appreciated for articles which are subsequently to be gilded. When such metal is required for rolling into sheet, it will be seen by reference to the table collated for the U.S. Board that the most malleable alloy is represented by the composition, 83 copper and 17 zinc. These alloys are also known by the name of red-brass, and as the reddish cast of colour is more agreeable to the eye than that of yellow-brass, they are frequently used for cast articles not requiring special hardness and strength. It has the reputation, however, of tarnishing quicker than ordinary brass. The properties of red-brass may be modified to suit special cases by the addition of tin, lead, and iron, the action of which has been already explained.

The following varieties of brass are distinguished from the preceding alloys by a characteristic yellow colour as contrasted with red-brass.

L