§ 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 analyses 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.

§ 36. Hamilton's Metal, Chrysorin, and Mosaic Gold.

Hamilton and Parker in 1826 claimed for the 50 per cent alloy that, after casting in the mould and cooling, it exhibits the colour of gold, and does not tarnish by exposure to air, even in the neighbourhood of the sea. They prepared it by fusing together equal parts of copper and zinc in a crucible at the lowest possible temperature, stirring constantly, and then adding a further quantity of zinc in small portions, till the right colour was obtained. This alloy is very flexible when strongly heated, but not adapted for cold rolling or wire drawing. It melts at a comparatively low temperature, and is used as a hard solder. The higher alloys given under the above names are malleable and ductile, and, as before mentioned, well adapted for cast ware.

The method of preparation described by Hamilton and Parker would be quite unsuitable for adoption on a working scale, for independently of the great waste of zinc, the composition of the alloy would be of an uncertain character. The usual plan is to melt the copper first and then add the zinc. The following plan has been recommended, but is open to serious objection for the same reasons as mentioned above. Bring into the crucible one-half of the zinc to be used; place upon this the copper, and fuse the mixture, under a cover of borax, at as low a temperature as possible. When the contents of the crucible are liquid, heat the other half of the zinc (cut into small pieces) until almost melted, and throw it into the crucible in portions; stir constantly to effect as intimate a mixture of the metals as possible.

§ 37. Prince's Metal.—A name given to various yellow alloys varying from 60 to 75 per cent of copper and 40 to 25 per cent zinc.

§ 38. Bobierre's Metal. This is ordinary brass, consisting of 66 parts copper and 34 parts zinc. Bobierre introduced this alloy as especially suitable for ships' sheathing.

§ 39. Macht's Yellow Metal is composed of 57 parts copper and 43 parts zinc. It has a reddish-yellow colour, malleable when rolled hot, but not in the cold. It is said to be suitable for fine castings, as it possesses great strength.

BRASS CONTAINING IRON

§ 40. Many samples of brass and bronze made by the ancients have been found on analysis to contain iron, and probably they knew that the addition of iron to these alloys would increase their hardness and strength, and introduced it with that view. In more modern times the combination of iron with brass has engaged the attention of metallurgists, and several alloys, containing iron as an essential constituent, have been introduced from time to time. In 1779 James Keir proposed an alloy of 10 parts iron, with 100 parts

copper and 75 parts zinc. Similar alloys to this, but containing less iron and different proportions of copper and zinc, were introduced under the names of "sterro-metal" or "Gedge's alloy," and "Aich's metal." Sir John Anderson, late superintendent of the royal gun factories, carried out a series of experiments with brass containing iron, and obtained some good results. The increased strength and hardness of such alloys were acquired at the expense of ductility and toughness. The great difficulty the above experimenter had to contend with was the uncertainty in the properties of the alloys containing iron.

§ 41. "Sterro-metal" consists of 60 parts copper, 38 to 38.5 zinc, and 2 to 1.5 iron. It was recommended / as an alloy for sheathing for ships and other objects which are subjected to the continued action of sea-water. The presence of iron in this alloy imparts to it a strength equal to that of mild steel, and superior to that of wrought-iron. Brannt mentions a case in which a wrought-iron pipe broke with a pressure of 267 atmospheres, while a pipe of sterrometal stood the enormous pressure of 763 atmospheres without cracking. This alloy also possesses great elasticity, and is therefore specially adapted for hydraulic cylinders. Such cylinders, when subjected to very high pressures, begin to sweat, the water from the inside permeating the pores of the metal. With sterro-metal the pressure can be raised considerably higher than with iron or steel, without moisture appearing on the outside of the cylinder.

Sterro-metal can be made very hard and dense by suitable mechanical treatment, which has as great an influence in modifying its properties as has the chemical composition. In rolling or hammering this alloy when hot, special care is requisite in regulating the temperature to which it is raised, as by too much heat it becomes brittle, and cracks under the hammer, or between the rolls. Baron Rosthorn tested a sterro-metal containing copper 55:04, zinc 42:36, tin 0.83, and iron 1.77 per cent, which gave the following results :

The tenacity of ordinary gun-metal is given for comparison. The specific gravity of the alloy was from 8:37 to 8.40 when forged or drawn into wire. Another alloy from the same source contained copper 55, zinc 41 34, and iron 3.66 per cent.

§ 42. Aich's Metal. This alloy is analogous to sterrometal, and shows similar variations in composition from various analyses that have been made. Its chief properties are hardness and tenacity, the same remarks applying to this as to sterro-metal, with which it is practically identical. Alloys under this name contain from 0.4 to 3.0 per cent of iron. It has a golden-yellow colour, and is recommended for articles exposed to sea-water. The following analyses will give an idea of the composition:

§ 43. Delta-metal.—This alloy was brought out by Mr. Alexander Dick in 1883, and since that time has established a useful place for itself among modern brasses. The name "delta" was given to it by Mr. Dick, simply for the purpose of connecting it with his own name, delta being the Greek for the letter D, the initial of the inventor's surname.

As already mentioned, the great difficulty former experimentalists had to contend with, was the uncertainty in the properties of the alloys containing iron, and Mr. Dick set himself the task of ascertaining the cause of failure. He prepared various quantities of the alloy, apparently in exactly