borax added, in order to prevent oxidation.

For white

alloys, the best proportions are within the following limits:

The proportion of zinc is increased if toughness and hardness are desired. More tin increases the malleability, whiteness, and lustre. But the proportion of lead should

not much exceed the amount indicated above.

§ 100. Alloys of Tin and Antimony. These metals when united together form the base of what is termed Britannia metal, many varieties of which consist of tin hardened by antimony. Such alloys are as white as tin, but harder and less malleable. The brittleness increases as the proportion of antimony is greater. Guettier states that the specific gravity of tin-antimony alloys is below that which would be calculated from the specific gravity of each metal taken singly. This indicates that expansion takes place by the union of these metals. An alloy of 80 parts tin and 20 of antimony is sufficiently malleable to be hammered and rolled in the cold. It is by keeping near these proportions that the best alloys of tin and antimony, for making pots and engravers' plates, are obtained. A white metal desertspoon analysed by the author was found to contain—

According to Chaudet, 10 parts tin to 1 part antimony form a perfectly ductile alloy.

Alloys of tin and antimony are made by fusing the two metals together. Also they may be made by reducing sulphide of antimony in contact with tin.

§ 101. Britannia Metal.—Reference has just been made to some alloys called by this name, consisting of tin and antimony, but more generally other metals in small quantities are added to the mixture, such as copper, zinc, lead, bismuth, etc. Britannia metal has a white colour, with a bluish tint ; it takes a high polish, is hard, malleable, and ductile in proportion to the amount of tin and copper present. The latter metal, however, must always be limited in quantity, as it tends to impart a yellowish tint, and diminish the fusibility, for which reasons the quantity of copper used is always very small compared with the tin and antimony. Good alloys show a fine-grained jagged fracture. If the alloy exhibits a crystalline fracture, it either contains too much antimony, or requires to be remelted in order to promote more intimate union of the constituents. Iron and zinc appear to be very objectionable, as they considerably increase the hardness and brittleness. If much zinc is used to make a cheap alloy, the antimony must be in much

smaller amount than is usual with better alloys. Lead is advantageous in cast work, making the alloy more fusible, but it impairs the colour and lustre, and the alloy tarnishes more readily in air than in alloys in which lead is absent. Arsenic, even in small quantity, induces brittleness, and should be avoided as much as possible. Alloy's containing metals other than tin and antimony are less brilliant in lustre than when these two metals alone are employed. The following table shows the composition of a few varieties of Britannia metal :

alloys having certain desired properties, but the use of commany other combinations are employed to produce white In addition to the alloys given in the preceding table

plicated alloys is much to be deprecated, for, as a rule, the stability is much greater the simpler the mixture; and although a useful alloy may be produced by careful manipulation, the proportions are disturbed when the scrap is remelted, or mixed with new metal and remelted. The author would therefore recommend a triple mixture of tin, antimony, and copper in preference to a more complex one, especially for wrought work.

The preparation of Britannia metal is based on the idea of rendering tin harder, tougher, more sonorous, and more easily polished. It furnishes castings as fine and sharp as those made with the most fluid alloys of tin and lead, copper and zinc, etc. It acquires a finer polish than alloys of tin and lead, because the latter is too soft to bear the action of emery and other polishing materials. A little brass is sometimes added, and bismuth increases the fusibility. The following proportions will serve as a guide :—

These are melted together; then the alloy so formed is fused with 15 to 20 per cent more tin, according to the judgment of the operator. A very complex alloy, termed by the inventor English metal, consists of—

Britannia metal is best prepared by melting the copper first, then adding the antimony with a portion of the tin, and finally adding the remainder of the tin. The mixture requires to be vigorously stirred in order to thoroughly incorporate the contents. If the alloy upon fracture shows a nonhomogeneous structure, it requires to be rapidly remelted under a layer of charcoal, to prevent oxidation. Certain alloys are very elastic, and well fitted for making wire.

In