Platinum vessels for chemical operations generally contain iridium, which makes them stronger and harder.

§ 173. Alloys of Platinum with easily fusible Metals. Platinum readily unites with arsenic and antimony, the combination being attended with vivid incandescence, forming brittle and easily fusible alloys.

Tin unites with platinum when the metals are fused together in equal parts, forming a hard, dark-coloured, somewhat fusible, brittle, and coarse-grained alloy.

Zinc unites with platinum forming an alloy of similar properties to the above-mentioned tin alloy.

Platinum and Lead readily unite, and very little lead makes platinum brittle. When molten lead is poured upon platinum, a portion of the latter is fused and dissolved in the lead. The alloys are hard, brittle, and granular.

Platinum and Bismuth form brittle alloys. Mr. Lewis found that the alloys ranging from 1 to 24 parts of bismuth to 1 of platinum are brittle, easily fusible, and have a laminar fracture. By contact with air they acquire a purple or violet tint. When moderately heated some of the alloys undergo liquation, the bismuth partially separating out. When strongly heated in air the bismuth largely burns off, forming bismuth oxide.

Platinum heated with Cadmium till the excess of the latter is volatilised forms a silver-white, very brittle, finegrained alloy, refractory in the fire, and containing 46 per cent of platinum.

§ 174. Platinum and Nickel.-According to Lampadius, equal parts of nickel and platinum unite to form a pale yellowish-white alloy, perfectly malleable, susceptible of a high polish, equal to copper in fusibility and to nickel in magnetic power.

§ 175. Platinor.—This is a name given to certain alloys containing platinum, of a golden-yellow colour, and consisting of platinum, copper, silver, zinc, and nickel. An alloy

of the colour of gold, and said to be quite constant in air, is prepared as follows: Melt 10 parts of silver with 45 parts of copper, then add 18 parts of brass and 9 parts of nickel. The temperature must then be raised to the highest pitch, and 18 parts of platinum-black added.

§ 176. Platinum-Bronze.-Several alloys of platinum, of a comparatively inexpensive nature, have been manufactured under the above name; and it has been claimed for them that they are indifferent to the action of the air and water. They admit of a high polish, and retain their lustre for a long time. The following table shows their composition

CHAPTER XII

IRON AND STEEL ALLOYS

§ 177. The general impression in the past has been that alloys of iron are of little importance, which was due to an imperfect acquaintance with their nature and properties; but at the present time there is more light being thrown on the subject, and if we expand the idea of an alloy so as to include those compounds in which very small quantities of other metals, such as aluminium, are present, then the alloys of iron may be considered of very great importance.

As a rule, iron may be alloyed with most metals; but the combination is somewhat difficult to effect, and, in the majority of cases, only those alloys with a small quantity of iron, or iron with a small quantity of other metals, have been found to have useful applications. Iron, added to other metals or alloys, imparts new and sometimes important properties, such as increased hardness, elasticity, and tenacity. Many of the more recently discovered metals have of late years been added to iron with more or less marked alteration in its qualities, and such combinations are now ordinary commercial articles.

In the following description of iron alloys, the metals known as "malleable-iron," "cast-iron," and "steel" are not treated as separate metals, but considered as different varieties of iron.

§ 178. Iron and Manganese.-Our knowledge of the

alloys formed by these metals has been greatly increased within the last few years by the labours of Mr. R. A. Hadfield of Sheffield. Iron readily unites with manganese, and when the proportion of the latter metal is considerable, the alloy is very hard, whiter, more fusible, and much more brittle in character than iron. In small quantity, up to 4 or 5 per cent, manganese is highly beneficial in steel, and some of the very best steel is that containing a little manganese. Steel containing from 2 to 7 per cent of manganese is brittle and comparatively worthless, but when the amount exceeds 7 per cent, alloys possessing very great strength and toughness are obtained.1 The weakness of the low percentage alloys may be understood from the following tests made by Mr. Hadfield. Cast-bars 2ğ inches square and 30 inches long, supported on bearings 2 feet apart, were broken by hydraulic pressure. One specimen containing 37 per cent of carbon and 4.45 per cent of manganese was fractured by a pressure of 33 tons, whilst a bar of ordinary cast-iron stood 12 tons, and bars containing 17 to 20 per cent manganese stood a pressure of 291 and 38 tons respectively. A cast-bar containing 4.73 per cent manganese, when dropped from a height of 3 or 4 feet on to a cast-iron floor, broke in two or three places. A sample containing 48 per cent carbon and 4.9 per cent manganese, though very ductile while hot, could be reduced to powder by a hand-hammer when cold, little or no cohesion seeming to exist between the particles. On the other hand, a specimen of forged material, containing 13.75 per cent manganese and 85 per cent carbon, when water toughened had a tensile strength of 65 tons per square inch, with 50 per cent elongation; another specimen had a strength of 69 tons, and 46 per cent elongation. The strongest alloy contains about 14 per cent of manganese.

When manganese-steel is plunged into water no hardening effect takes place like that of ordinary steel, but the metal 1 Hadfield. Paper on Manganese Alloys. I. C. Eng. 28th February

1888.

containing upwards of 7 per cent of manganese acquires increased tenacity and toughness. From a large number of tests it has been found that the higher the temperature to which the alloy is raised, and the more suddenly the cooling takes place, the higher is its breaking stress, and the greater its toughness and elongation. The influence of water quenching on manganese-steel is strikingly shown in alloys required to be drawn into wire. If it be attempted to draw hammered or rolled rods into wire without a previous heating and quenching it will not draw at all, and ordinary annealing makes no difference to it. If, however, it be raised to a yellow heat and then plunged into cold water it can be readily drawn into wire. After reducing the wire two numbers of the gauge, the metal is again heated and plunged into water. By this means it may be drawn to any reasonable degree of fineness.

The density of manganese-steel is a little higher than that of ordinary steel. In its ordinary condition it is very hard and easily scratches steel that is not highly tempered. When the manganese exceeds 20 per cent the alloy is practically non-magnetic. Dr. Hopkinson found that the maximum magnetisation of wrought-iron and manganese steel (with 12.36 per cent of manganese) are as 258 to 1. It shows no elongation under the magnetic influence.

Manganese-steel does not exhibit the anomalous expansion and " "after-glow," termed re-calescence, which takes place in magnetic metals when they cool to a certain critical temperature, after being heated to whiteness. A Sheffield firm reported that in rolling a considerable length of manganese-steel, the finer it became the more it retained its heat, in fact, it appeared to gather heat in the process.

Ferro-Manganese is a variety of metal specially manufactured in a blast furnace from ores rich in oxide of manganese, and is very extensively used in the manufacture of mild steel. When the pig-iron contains less than about 20 per cent manganese, its fracture shows large crystalline