The marginal numbers denote the ounces of tin added to every pound of copper.

Modern Copper and Tin Alloys.

1 oz. Soft gun metal, that bears drifting, or stretching from a perforation.

1 1/3 oz. A little harder alloy, fit tor mathematical instruments; or 12 copper and 1 very pure grain tin.

1 1/2 oz. Still harder, fit for wheels to be cut with teeth.

1 1/2 to 2 oz. Brass ordnance, or 8 to 12 per cent. tin; but the gen-eral proportion is one-ninth part of tin.

2 oz. Hard bearings for machinery.

2 1/2 oz. Very hard bearings for machinery. By Muschenbroek's Tables it appears that the proportion 1 tin and 6 copper is the most tenacious alloy; it is too brittle for general use, and contains 2 1/4 oz. to the pound of copper.

3 oz. Soft musical bells.

3 1/2 oz. Chinese gongs and cymbals, or 20 per cent. tin.

4 oz. House bells.

4 1/2 oz Large beds.

5 oz. Largest bells.

7 1/4 to 8 1/4 oz. Speculum metal. Sometimes one ounce of brass is added to every pound as the means of introducing a trifling quantity of zinc, at other times small proportions of silver are added; the employment of arsenic is by some recommended.

The object agreed upon by all experimentalists appears to be the exact saturation of the copper with the tin, and the proportionate quantities differ very materially (in this and all other alloys), according to the respective degrees of purity of the metals: for the most perfect alloys to this group, Swedish copper, and grain tin, should be used.

"When the copper is in excess, it imparts a red tint easily detected; when the tin is in excess, the fracture is granulated and also less white. The practice is to pour the melted tin into the fluid copper when it is at the lowest temperature that a mixture by stirring can be effected, then to pour the mixture into an ingot and to complete the combination by remelting in the most gradual manner, by putting the metal into the furnace as soon almost as the fire is lighted: trial is made of a little piece taken from the pot immediately prior to pouring.

32 oz. of tin to one pound of copper, makes the alloy called by the pewterers "temper" which is added in small quantities to tin, for some kinds of pewter, called "tin and temper" in which the copper is much less than 1 per cent.

Remarks on the Alloys of Copper and Tin only.

These metals seem to mix in all proportions.

The addition of tin continually increases the fusibility, although when it is added cold it is apt to make the copper pasty, or even to set in a solid lump in the crucible.

The red color of the copper is not greatly impaired in those proportions used by the engineer, namely, up to about 2 1/2 ounces to the pound; it becomes grayish white at 6, the limit suitable for bells, and quite white at about 8, the speculum metal; after this, the alloy becomes of a bluish cast.

The tin alloy is scarcely malleable at 2 ounces, and soon becomes very hard, brittle, and sonorous; and when it has ceased to serve for producing sound, it is employed for reflecting light.

The tough tenacious character of copper under the tools rapidly gives way; alloys of 1 1/2 cut easily, 2 1/2 assume about the maximum hardness without being crystalline; after this they yield to the file by crumbling in fragments rather than by ordinary abrasion in shreds, until the tin very greatly predominates, as in the pewters, when the alloys become the more flexible, soft, malleable, and ductile, the less copper they contain.