x5o On the Effi5l of a Mixture of Tin with Gold. 



of curvature, or bring it to the flexibility it would have pofleffed if no tin had entered into 

 its compofition. Hence I clearly faw, that this rigidity announced a diminution of its 

 du£tility ; that the interpofition of a fubftance, which was foreign to the gold, and inca* 

 pable by its nature of maintaining the cohefion, was the caufe of this want of flexibility ; 

 and sthat it could be attributed only to the tin, becaufe copper alone, mixed with fine gold, 

 though it gives a greater degree of hardnefs and rigidity than it before pofleffed, deprives it 

 of very little of its ductility. 



After this firfl obfervation on the ftate of the ingot afforded by the experiment, I came 

 to the more decifive proof by hammering, particularly vs^ith the edge of the hammer, in or- 

 der that the bar might be lengtliened, and by that means fubmitted to the molt decifive 

 proof. I did not obferve during the continuation of this proccfs, till the bar was reduced 

 to about two-thirds of its firft thickncfs — I did not obferve, I fay, that its edges were 

 cracked, or exhibited much of the appearance of brittlenefs ; but as I was apprehenfive 

 that this accident might happen by too long hammering, I divided the bar by cutting off 

 the part which had been hammered out. This part was placed in the midfl of lighted 

 charcoal, in order that, by a moderate annealing, it might recover the ftate of malleability 

 it poffeffed before it was hammered. 



But when I went to take it out of the fire, where it had undergone no greater heat than 

 a cherry-red, I found it divided into two parts. After having fuffered thefe to cool, I 

 forged them again. They were extended with confiderable eafe, though with fome cracks 

 at the edges ; but they did not yet fatisfy the whole of my enquiries. I therefore annealed 

 one of the two laft-mentioned pieces a fecond time, and referved the other in its hard 

 hammered ftate to be paffed between the laminating rollers. The annealed part, which 

 might have the thicknefs of about a ftiilling (piece de douze fols), broke in the fire, though 

 the heat was very gentle, into four or five portions. The longeft of thefe portions, which 

 beft refifted the action of the fire, bent and twifted itfelf, and fhewed, by this ftate of 

 ftrong contradtion in different diredtions, that it had tended to break and become divided 

 into fmall portions fimilar to thofe which had already feparated from it. 



This accident gave me reafon to fufpeft that the aflies, upon which I had annealed the 

 plate of gold which broke -in pieces, might alfo contain certain portions. I was not de- 

 ceived ; for the aflies being carefully waftied left three or four fragments which the ignited 

 coals had prevented from being feen. 



It has been remarked, that I referved orte of the two parts of the portion of the ingot 

 which I had forged a fecond time, and that I had kept it in its hammer-hardened ftate. I 

 could not doubt, after the laft-recited experiment, that any attempt to anneal this portion, 

 even by the moft moderate heat, would be attended with the fame confequence, namely, 

 that it would break in pieces. I therefore detcrniined to extend it ftill more between the 

 rollers, fetting them up very gradually in order that the fracture, if it fliould take place, 

 might be principally owing to the brittlenefs of the material, and not to the force of com— 

 preflion to which it was fubjefted. By this management 1 fucceeded in extending the 

 nietal to double its length notwithftanding its hardnefs. In this manner it was rendered 

 as thin as ftrong paper ; though it muft be ccnfeffed that the edges were cracked through 

 their whole length like the teeth of a faw. But this accident is not at all furprifing, when 

 it is confidercd that gold, though alloyed Cmply with coppet, whatever may be the caufe, 



does 



