ALLOY 



There are many points of great physical as well as chemical interest in connection 

 with alloys, which require a closer study than they have yet received. There aro 

 some striking facts, brought forward by M. Wertheim, deduced from experiments 

 carried on upon fifty-four binary alloys and nine ternary alloys of simple and known 

 composition, which will be found in the ' Journal of the French Institute,' to which 

 the reader desiring information on this point is referred. 



It is hardly possible to infer the melting point of an alloy from that of each of its 

 constituent metals ; but, in general, the fusibility is increased by mutual affinity in 

 their state of combination. Of this a remarkable instance is afforded in the fusible 

 metal consisting of 8 parts of bismuth, 5 of lead, and 3 of tin, which melts at the heat 

 of boiling water, or 212 F., though the melting point deduced from the mean of its 

 components should be 614 F. This alloy may be rendered still more fusible by 

 adding a little mercury to it, when it forms an excellent material for anatomical injec- 

 tions. See FUSIBLE METAL. 



On the Melting Point of Certain Alloys. 



Centigrade 

 Thermometer. 



Lead 334 



Tin 230 



Tin, 5 atoms ; lead, 1 atom . 194 

 4 1 . 189 



, 3 1 186 



Centigrade 

 Thermometer. 



Tin, 2 atoms ; lead, 1 atom . 196 

 1 1 . 241 

 1 3 . 289 

 2 vols.; 1 vol. . 194 



In these experiments of M. Kupffer, the temperatures were determined with ther- 

 mometers of great delicacy, and the weighings were carefully carried out. Ann. de 

 Chimie, xl. 285-302 ; Brewstcr's Edin. Jour. ScL i. N.S. p. 299. 



The colours of alloys do not depend in any considerable degree upon those of the 

 separate metals ; thus, the colour of copper, instead of being rendered paler by a large 

 addition of zinc, is thereby converted into a rich-looking yellow metal, brass. 



By means of alloys, we multiply, as it were, the number of useful metals, and 

 sometimes give usefulness to such as are separately of little value. Since these com- 

 pounds can be formed only by fusion, and that many metals are apt to oxidise readily 

 at their melting temperature, proper precautions must be taken in making alloys to 

 prevent this occurrence. Thus, in combining tin and lead, resin or grease is usually 

 put on the surface of the melting metals, the carbon produced by the decomposition 

 of which protects them, in most cases, sufficiently from oxidation. When we wish 

 to combine tin and iron, as in the tinning of cast-iron tea-kettles, we rub sal-ammo- 

 niac upon the surfaces of the hot metals in contact with each other, and thus exclude 

 the atmospheric oxygen by means of its fumes. When there is a notable difference 

 in the specific gravities of the metals which we wish to combine, we often find great 

 difficulties in obtaining homogeneous alloys ; for each metal may tend to assume the 

 level due to its density, as is remarkably exemplified in alloys of gold and silver made 

 without adequate stirring of the melting metals. If the mass be largo and slow of 

 cooling, after it is cast in an upright cylindrical form, the metals sometimes separate, 

 to a certain degree, in the order of their densities. Thus, in casting large bells and 

 cannon with copper alloys, the bottom of the casting is apt to contain too much 

 copper and the top too much tin, unless very dexterous manipulation in mixing the 

 fused materials has been employed immediately before the pouring out of the melted 

 mass. When such inequalities are observed, the objects are broken and re-melted, 

 after which they form a much more homogeneous alloy. This artifice of a double 

 melting is often had recourse to, and especially in casting the alloys for the specula 

 of telescopes. 



When we wish to alloy three or more metals, we often experience difficulties, 

 either because one of the metals is more oxidisable, or denser, or more fusible, than the 

 others, or because there is no direct affinity between two of the metals. In the latter 

 predicament, we shall succeed better by combining the three metals first in pairs, 

 for example, and then melting the two pairs together. Thus, it is difficult to unite 

 iron with bronze directly ; but if, instead of iron, we use tin plate, we shall imme- 

 diately succeed, and the bronze, in this manner, acquires valuable qualities from 

 the iron. Thus, also, to render brass better adapted for some purposes, a small 

 quantity of load is sometimes added to it, but this cannot be done directly with 

 advantage ; it is better to melt the lead first along with the zinc, and then to add 

 this alloy to the melting copper, or the copper to that alloy, and fuse them together. 



One of the alloys most useful to the arts is brass ; it is more ductile and less easily 

 oxidised than even its copper constituent, notwithstanding the opposite nature of the 

 zinc. (See BRASS.) This alloy may exist in many different proportions, under which 



