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:—

I

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 30 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

the same way, by dissolving wrought-iron in molten copper. The results showed many discrepancies, because the amount of iron dissolved in each sample was far from uniform. He then tried to find a method by which he might be enabled to introduce a known and definite quantity of iron, and succeeded by dissolving iron in molten zinc to saturation, and adding the same, with or without pure zinc, to the molten copper. But when the metals were remelted, oxidation took place, and the castings again varied in character, owing to the oxides thus formed dissolving in the alloy, and diminishing its strength and toughness. This second difficulty was overcome by adding a small percentage of phosphorus in combination with copper. In some cases Mr. Dick also introduces tin, manganese, or lead into the alloy, to impart special properties to it. The various alloys thus produced are now manufactured and sold under the name of "delta"-metal. The inventor claims that by his process the iron is chemically combined in the brass and bronze, as proved by the alloys not rusting when exposed to moist air, and by their indifference to the magnetic needle.

In a lecture by Mr. Macintyre before the Balloon Society on 15th November 1889, he states that "the properties which are combined in delta - metal — great strength and toughness, durability, resistance to corrosion, and a comparatively low price-render it of the greatest value for purposes of construction generally; and more especially for shipbuilding, marine engineering, and sanitary work. It can be equally well cast as forged, stamped and rolled hot, and drawn cold."

The power of delta-metal to resist corrosion by the acid liquors of mines has been proved by the Bonifacius Coal Mining Company of Westphalia. The Company made a series of experiments with a view to finding the relative corrosion of metals of suitable strength. Brass and gun-metal were not strong enough, and trials were made with steel, iron, and delta-metal. Rolled bars of each of these were immersed during a period of six and a half months in the water issuing

from the pits at Kray, and then carefully re-weighed and

photographed. The bars were 7 sectional area of 62 square inches.

inches long, and had a The following were the

weights of the three kinds of bars before and after the trial :-

In the Schweizerisches Gewerbeblatt of 8th June 1889 the following tests of delta-metal were recorded: "In the first locomotive engines of the Pilatus mountain railway, a material was required which could be cast, and possess at the same time great tensile strength and elasticity. Delta-metal was found to answer these requirements; the worm-wheels of the brake gear for the engines were of this material and worked very satisfactorily. The castings were tested by Professor Tetmayer of Zürich, the results showing a tensile strength of 21 to 23 tons per square inch, with an elongation of 30 to 40 per cent on a length of 77 inches." Captain Locher also had the following tests made: One of the delta-metal pinions having been in use for a long time, the teeth had worn about of an inch, so that their thickness at the root was ğ inch, and at the top inch, by a breadth of 47 inches. It was tested to show what power would be required to break such a tooth. The test, made by Professor Tetmayer, gave the following result :—

P.

AL

5 9 10 12 14 15 16 17 18 0 0.015 0.019 0.059 0.098 0.133 0.169 0.208 0.244 P. 19 20 21 211

AL 0.295 0.354 0.472 | broke.

P indicating the stress in tons, and AL the shortening in decimals of an inch of the distance L originally measuring 22 inch. Both as regards P and AL the results were unexpectedly favourable.