In chemical combinations it is a well-known fact that elements always combine with other elements in definite proportions by weight, termed atomic weight, producing compounds of fixed and decided properties, so that the same compounds can be always relied upon to contain the same elements, united in the same proportions. This same law applies to the union of two metals, when such metals are chemically combined, and the same alloy will always have properties identically the same, however it may be tested. Several experimenters have directed their attention to the mixing of metals according to their atomic weights, so as to obtain alloys of determined characteristic properties, but up to the present time the number of such combinations of a useful character is very limited. They are by no means the ones most suited to the wants and requirements of industry. There is always one indispensable item from the manufacturer's point of view which the chemist is not concerned with—that is, the cost of production-and however nicely atomic proportions would suit the requirements of a given alloy, such an alloy would in most cases be useless unless the cost was consistent with the market value. The question then of cost must have consideration, and the proportions must, if possible, be made to fit in with commercial necessities. With regard to copper alloys, such as brass and bronze, the combinations which best exhibit the characters of chemical compounds are hard and brittle, and as copper alloys are much more widely used than any other, there is little inducement to encourage metallurgists to endeavour to alloy copper and zinc, or copper and tin in atomic proportions, since malleability and tenacity are the properties most desired in these alloys. Again, colour is the chief desideratum in many alloys, and this cannot be always obtained by mixing in atomic proportions, especially as it often happens that a very small addition of one of the constituents will alter the shade of colour, so as to produce what is required.

When it is desirable to add a non-metallic element to a

metal or alloy, for the purpose of bringing about a certain result, very much greater care is generally required in apportioning the quantity to be added than with a metal, as non-metals combine much more actively with metals than the metals do with each other, and a very small quantity of a non-metal will suffice to alter the properties of a metal or alloy. It is very surprising to note how, in some instances, a mere trace of another element will alter the properties of a metal. For example, of carbon added to iron will convert it into mild steel; 1000 of phosphorus makes copper hot - short; 2000 part of tellurium in bismuth makes it minutely crystalline; 1000 part of antimony in copper renders it exceedingly bad in quality for certain purposes.

207 11.45

=

1

Lothar Meyer has shown that a remarkable relation exists between the "atomic volumes of the elements." The relative atomic volumes of the elements are found by dividing their atomic weights by their specific gravities. The atomic weight of lead is 207, and its specific gravity 11.45; = 18, the atomic volume of lead. It would appear that the power of an element to produce weakness in a metal, when added in small quantity, is dependent on the atomic volume of the impurity.1 Roberts-Austen tried the effect of various elements on pure gold, and found that when the body added had an atomic volume equal to, or less than that of gold, the strength was little affected, and in some cases, as copper for example, was increased; but when the element added had an atomic volume much greater than that of gold the strength, with two exceptions, was greatly diminished. His results are embodied in the following table:

1 Journal of Soc. of Arts, 19th October 1888.

Alloys generally have properties differing from their constituents, and some have these differences very strongly marked, thus: if a very small quantity of arsenic be added to tin, the resulting alloy will have a crystalline fracture closely resembling zinc. Sometimes metals combine with evolution of heat and sometimes with an absorption of heat. The following metals, according to Roberts-Austen, evolve heat when they are united :-aluminium and copper, platinum and tin, arsenic and antimony, bismuth and lead, gold and just melted tin. On the other hand, lead and tin when

they unite absorb heat.

When lead, tin, and bismuth in equivalent proportions, and very finely divided, are mixed with eight equivalents of mercury, at the ordinary temperature, the temperature will fall from 17° C. to -10° C. If the vessel containing the mixture stand on a wet board the water underneath will be frozen. This combination then will form a freezing mixture.

The method of producing alloys by strongly compressing

the powders of the constituent metals was shown by Professor Spring of Liège in 1878, and he has since devoted much study to the subject. His experiments were made by the aid of a press, the form of which is shown in Fig. 4. The metallic powder is placed under a short cylinder of steel, in the cavity of a steel block divided vertically, held together by a collar, and placed in a chamber of gun-metal, which

may be rendered vacuous.

FIG. 4.

The pressure is applied to a cylindrical rod passing through a stuffing-box. Under a pressure of 2000 atmospheres, or 13 tons to the square inch, lead, in the form of filings, becomes compressed to a solid block; and under a pressure of 5000 atmospheres the metal flows through all the cracks of the apparatus like a liquid. Spring obtained some important results with crystalline metals, such as bismuth and antimony. At a pressure of 6000 atmospheres finely powdered bismuth unites

1 Bul. de l'Acad. de Belgique (2), tom. xlv. No. 6, 1878; (2) tom. xlix. No. 5, 1880.

into a solid mass, having a crystalline fracture. Tin when similarly compressed in powder, is made to flow through a hole in the base forming a wire. The following table shows the amount of compression required to unite the powders of the respective metals :—

It occurred to Professor Spring that the particles of different metals might be united by pressure, so as to form alloys, and he considered that the formation of such alloys by pressure would afford conclusive proof that there is true union between the particles of metals in the cold, when they are brought into intimate contact. He compressed a mixture of 15 parts bismuth, 8 parts lead, 4 parts tin, and 3 parts cadmium, and produced an alloy which fuses at 100° C. It is necessary to crush up the product of the first compression, and again submit the powder to compression, in order to get a perfect alloy. The objection has been urged that the mixture may have been fused by the heat of compression. Professor Spring has experimentally proved that this was not the case. The compression was effected with extreme slowness, and he calculates that if all the work done in compressing the powders were translated into heat, it would only serve to heat a cylinder of iron 10 mm. in height and 8 mm. in diameter 40·64° C. Spring took the organic compound phorone, which melts at 28° C., and compressed it in precisely the same way as the metallic powders. Only imperfect union of the particles resulted, and the 28° of heat necessary to melt the phorone was not generated.1

1 Bul. Soc. Chim. Paris, 1884, tom. xli. p. 488.