It will be seen from the foregoing table that the addition of nickel to mild steel increases the elastic limit and breaking stress considerably. In Nos. 2 and 5 tests the extreme hardness, partly due to the large amount of carbon, is also increased by the presence of nickel. In No. 9 test, with much less carbon, but with 10 per cent nickel, a very hard alloy is obtained. This quality of hardness continues as the nickel is increased, until about 20 per cent is reached, when a change takes place, and successive additions of nickel tend to make the steel softer and more ductile. With regard to the hardening effect of nickel on iron there is some resemblance to the manganese-steel previously described. The whole of the series of nickel-steels up to 50 per cent nickel take a good polish and finish, with a good surface, the colour being lighter with the increased additions of nickel.

Mr. Riley states that the steels rich in nickel are practically non-corrodible, and that those poor in nickel are much better than other steels in this respect. The 1 per cent nickel-steel welds fairly well, but this property deteriorates with each addition of nickel. Mr. Hall states that the alloys of nickel and iron are among the most powerful connected with the magnet that he has seen or heard of. The conductivity for electricity of iron-nickel alloys is extremely low, and the electric resistance extremely high.

The alloys of iron and nickel may be prepared by melting iron and nickel together; by reducing oxide of nickel with carbon in the presence of iron; or by adding ferro-manganese to molten iron and nickel to obtain nickel-steel. Mr. Riley states that without the aid of manganese the conditions of treatment would not be successful.

$180. Iron and Cobalt.-According to the experiments of Brande and Bergmann, these metals combine in all proportions. The alloys are said to be hard, and as ductile as iron. Hassenfratz has shown that iron containing cobalt can be forged and welded, and although a little brittle when hot, it is not so when cold. According to Berzelius, the

alloys of these metals are hard and magnetic. It is probable that the action of cobalt on iron is much the same as that of nickel, judging from the similarity of cobalt to nickel in many of its physical and chemical properties.

§ 181. Iron and Molybdenum.-Dr. Thompson considers that of all the metals, molybdenum is the one with which iron unites most readily. With equal parts of the two metals the alloy is fusible with the blowpipe. With 1 part iron and 2 parts molybdenum, an alloy of a clear grayish-white colour is obtained. An alloy of 20 per cent molybdenum is whiter than iron, very hard, brittle, tenacious, and has a granular fracture. Berthier considers the alloys of molybdenum and iron to be in every respect the analogues of those of tungsten and iron. They are generally grayishwhite, hard, brittle, fine-grained, and magnetic. When the molybdenum is below 50 per cent the alloys are somewhat fusible. Copper blast-furnace bears (as the metallic masses found in the hearths of old copper blast-furnaces are termed) chiefly consist of iron and molybdenum.

§ 182. Iron and Chromium.-These metals have a strong affinity for each other and appear to form alloys in all proportions. Chrome-iron ore is somewhat abundant in nature, and when such ore is submitted to a reducing influence at a high temperature both iron and chromium occur in the reduced metal. Berthier states that when a mixture of oxide of iron and oxide of chromium is strongly heated in a carbon lined crucible, both oxides are completely reduced, and a perfectly homogeneous combination of the two metals is obtained. The alloys are generally hard, brittle, crystalline, of a grayish-white colour, and having a considerable lustre; less fusible, less magnetic, and less soluble in acids than iron; the characters are the more prominent in proportion to the amount of chromium present in the alloys. In 1820 Faraday produced two specimens of chrome1 Quarterly Journal of Science, 1820.

steel. He states that both forged well, and were as malleable as pure iron, and that both gave a very beautiful damask when rubbed with sulphuric acid. From these results as to malleability, and also from the mixture used, the percentage of chromium must have been small. This damascening of chrome-steel is interesting when we consider that it is not producible with ordinary steel, and that it is only otherwise produced by taking extreme precautions in the working of the purer forms of malleable iron. 1 Schneider has shown that chrome pig-iron is not a homogeneous body, and the fact of the damascening being produced in the steel would indicate that the observation would also apply to it. Two alloys prepared by Berthier, one containing 1 and the other 15 per cent chromium, forged well, and made razor and sword blades of excellent quality.

M. Brustlein, of Unieux, France, commenced the manufacture of chrome-steel in 1875. Ferro-chrome is produced in crucibles and a certain proportion of this rich alloy is added to the steel. The usual specimens of the ferrochrome contain from 42 to 52 per cent of chromium. The metal is cast into iron moulds and chilled. The following table shows the composition per cent of different samples; and it is interesting to notice the large amount of carbon taken up by the alloys :

The remainder would be iron and silicon, the latter sometimes exceeding 2 per cent. The hardness and brittleness increase with the proportion of carbon and silicon. When ferro-chrome is cooled slowly it crystallises into a mass of needle-shaped crystals, which are more apparent when the carbon is low.

With regard to magnetism, chromium has a much less 1 Oesterreichische Zeitschrift für Berg und Hüttenwesen, 1886, tom. xxxiii. p. 29.

powerful effect in destroying the magnetic properties of iron than manganese, for iron containing 65 per cent of chromium is still attracted by a magnet.

In the manufacture of steel, varying proportions of chromium may be used. Brustlein states that steel containing 2 per cent carbon and 12 per cent chromium may be forged. The presence of chromium in steel increases its tenacity and imparts a higher resistance to pressure. It also renders steel harder to file or work on the lathe in proportion to the quantity of carbon present. Hardened steel containing chromium has a very fine grain, and breaks with a glassy fracture. Chrome-steel cannot be welded; it burns when highly heated, owing to the strong affinity of chromium for oxygen, and the oxide formed is infusible even at the melting-point of steel. From the above table it will be seen that ferro-chromes may be combined with exceptionally large proportions of carbon, and they may in consequence be used instead of ferro-manganese in making Bessemer or Siemens's steel. But extra soft steel, containing much chromium, is at present impossible. If ferro-chrome be made, having little carbon, it is very oxidisable, and almost infusible, so that many difficulties stand in the way of supplanting ferromanganese by ferro-chrome.

§ 183. Iron and Titanium.-Pig-iron sometimes contains titanium, when obtained from ores containing that metal, which often occur along with iron ores. The titanium is either minutely disseminated through the iron or alloyed with it. Some analyses by Mr. Riley of gray pig-iron from Wiltshire gave 1.15, 71, and 47 per cent of titanium respectively. But iron smelted from titaniferous iron-ore may be quite free from titanium. 1In 1877 Mr. Riley showed that the so-called titanium steel of Mushet 2 contained no titanium. Faraday failed to reduce titanium oxide, although he states that rhodium, and, imperfectly, platinum were melted

1 Iron and Steel Institute, 1887.
2 Mushet's patents, 1859 to 1861.

in the crucibles he used. In 1742 Mr. Horne successfully smelted the titaniferous ores of Canada, and good steel was made from them, the virtue of which was ascribed to this particular ore, although this was before titanium had been isolated as an element. It is a noted fact that titanium iron ores are practically free from phosphorus, which may readily account for the good quality of iron produced therefrom. We may consider then that titanium steel exists only in name. What titanium occurs in the pig-iron passes into the slag when the iron is refined.

§ 184. Iron and Tungsten.—These metals unite to form some valuable alloys. Steel containing tungsten is highly valued for cutting tools. Formerly, the oxide of tungsten and carbon were melted in crucibles with Swedish or good hematite pig-iron. The steel is now made by introducing a rich alloy, containing up to 50 per cent of tungsten, into the crucible or bath of metal. Tungsten steel is known in England as Mushet's special steel. It possesses a natural hardness of its own, and, when upwards of 3 per cent of tungsten is present, instead of being hardened by heating and quenching in water, like ordinary steel, it is actually softened. It is very difficult to forge, and cannot be welded when the tungsten exceeds 2 per cent; but can be cast into the form of tools, which can be ground to a fine edge. Tungsten gives to steel a very fine and uniformly crystalline structure, and such steel is less affected by the atmosphere than ordinary steel. 1 Mr. Stroh states that tungsten-steel possesses remarkable magnetic properties. He uses a 3 per cent tungsten alloy for telephone magnets with marked advantage. It is stated by several experimenters that tungsten imparts to cast-iron great hardness and tenacity, but Guettier found no advantage in adding tungsten to cast iron as regards resistance to shock or flection. The general concensus of opinion appears to be that tungsten in steel is valuable for certain purposes, but that the general method of 1 Transactions of Soc. of Telegr. Eng. 1882.