ALLOY 93 



it has different names, as tombac, similor, pinchbeck, &c. Copper and tin form 

 compounds of remarkable utility, known under tho name of hard brass, for the 

 bushes, steps, and bearings of the axles, arbours, and spindles in machinery; and 

 of bronze, bell-metal, &c. (See BBONZE, &c.) Gold and silver, in their pure state, arc 

 too soft and flexible to form either vessels or coins of sufficient strength and dura- 

 bility ; but when alloyed with a little copper, they acquire the requisite hardness and 

 stiffness for these and other purposes. Aluminium has been found by Dr. Percy to 

 possess the same hardening property. See ALUMINIUM BEONZE. 



When we have occasion to unite several pieces of tho same or of different metals, 

 we employ the process called soldering, which consists in fixing together the surfaces 

 by means of an interposed alloy, which must be necessarily more fusible than the 

 metal or metals to be joined. That alloy must also consist of metals which possess a 

 strong affinity for the substances to be soldered together. Hence each metal would 

 seem to require a particular kind of solder, which is, to a certain extent, true. Thus, 

 the solder for gold trinkets and plate is an alloy of gold and silver, or gold and copper; 

 that for silver trinkets is an alloy of silver and copper ; that for copper is either fine 

 tin, for pieces that must not be exposed to tho fire, or a brass alloy called hard 

 solder, of which the zinc forms a considerable proportion. The solder of lead and 

 tin plate is an alloy of lead and tin, and that of tin is the same alloy with a little bis- 

 muth. Tinning, gilding, and silvering may also be reckoned as species of alloys, 

 since the tin, gold, and silver are superficially united in these cases to other metals. 



Metallic alloys possess usually more tenacity than could be inferred from their con- 

 stituents ; thus, an alloy of 12 parts of lead with 1 of zinc has a tenacity double that 

 of zinc. 



The cohesive force of alloys is well shown in the annexed Table (p. 94), in which the 

 results are mostly those obtained by Muschenbroek. 1 



Metallic alloys are generally much more easily oxidised than the separate metals, a 

 phenomenon which may be ascribed to the increased affinity for oxygen which results 

 from the tendency of the one of the oxides to combine with the other. An alloy of 

 tin and lead heated to redness takes fire, and continues to burn for some time like a 

 piece of bad turf. 



Every alloy is, in reference to the arts and manufactures, a new metal, on account 

 of its chemical and physical properties. A vast field here remains to be explored. 

 Not above 60 alloys have been studied by the chemists out of many hundreds which 

 may be made ; and of these but few have been yet practically employed. Very slight 

 modifications often constitute valuable improvements upon metallic bodies. Thus, 

 the brass most esteemed by turners at the lathe contains from 2 to 3 per cent, of lead ; 

 but such brass does not work well under the hammer ; and, reciprocally, the brass 

 which is best under the hammer is too tough for turning. 



M. Chaudet has made some experiments on the means of detecting the metals of 

 alloys by the cupelling furnace, and they promise useful applications. Tho testing 

 depends upon the appearance exhibited by the metals and their alloys when heated 

 on a cupel. The following were Chaudet's results : 



Metals. Pure tin, when heated this way, fuses, becomes of a greyish-black colour, 

 fumes a little, exhibits incandescent points on its surface, and leaves an oxide which, 

 when withdrawn from the fire, is at first lemon-yellow, but, when cold, white. Anti- 

 mony melts, preserves its brilliancy, fumes, and leaves the vessel coloured lemon- 

 yellow when hot, but colourless when cold, except a few spots of a rose tint. Zinc 

 burns brilliantly, forming a cone of oxide ; and the oxide, much increased in volume, 

 is, when hot, greenish, but, when cold, perfectly white. Bismuth fumes, becomes 

 covered with a coat of melted oxide, part of which sublimes, and the rest enters the 

 pores of the cupel ; when cold, the cupel is of a fine yellow colour, with spots of a 

 greenish hue. Lead resembles bismuth very much ; the cold cupel is of a lemon- 

 yellow colour. Copper melts, and becomes covered with a coat of black oxide ; some- 

 times spots of a rose tint remain on the cupel. 



Alloys. Tin 75, antimony 25, melt, become covered with a coat of black oxide, 

 have very few incandescent points ; when cold, the oxide is nearly black, in con- 

 sequence of the action of antimony ; a 4^th part of antimony may be ascertained, 

 in this way, in the alloy. An alloy of antimony containing tin leaves oxide of tin 

 in the cupel ; a j^th part of tin may be thus detected. An alloy of tin and zinc 

 gives an oxide which, whilst hot, is of a green tint, and resembles philosopher's wool 

 in appearance. An alloy containing 99 tin 1 zinc did not present the incandescent 

 points of pure tin, and gave an oxide of greenish tint when cold. Tin 95, bismuth 5 

 parts, gave an oxide of a grey colour. Tin and lead give an oxide of a rusty brown 

 colour. An alloy of lead and tin, containing only 1 per cent, of the latter metal, when 



Encyclopedia Britannica, Art. STUENGIH, and introduction ad Philoso. Natures. 



