624 PHILOSOPHICAL TRANSACTIONS. [ANNO 1784, 



operation 6 grains only were lost in the weight ; and the bar obtained was no less 

 manufacturable than at first. 



Exper. 8 and 9. The mixtures of gold and tin, from the 2d and 4th experi- 

 ments, were re-melted separately, and 1 oz. of copper added to each. Being 

 both well stirred, they were cast as usual ; and the bars, though sensibly harder, 

 bore all the operations of manufacturing as before. The last bar cracked a little 

 at the edges, on drawing through the rollers, as it had done without the copper, 

 but not materially, and bore cutting rather better than in its former state. 



Exper. 10 and 11. A quarter of an ounce of the last mixture (being tin 1 an 

 oz. and copper 1 oz. with gold 1 2 oz.), and as much of the bar from the 3d 

 experiment (being tin 120 grs. with gold 12oz.) were each melted by a jeweller, 

 in the most ordinary manner, with a common sea-coal fire, into small buttons, 

 without any loss of weight. These buttons were forged by him into small bars, 

 nealing them often by the flame of a lamp, and afterwards drawn each about 20 

 times through the apertures of a steel plate, into fine wire, with as much ease as 

 coarse gold commonly passes the like operation. 



Exper. 12. To inquire whether the adding of tin to gold, already alloyed, 

 would cause any difference, 60 grs. of tin were stirred into 12oz. of standard 

 gold, -J4 fine ; and the result passed every operation before described, without 

 showing the least alteration from the tin. 



For greater certainty, several other trials were made, of different mixtures of 

 copper, tin, and silver, with gold, even so low as 2-J- oz. of copper, with \ an 

 oz. of tin, to 12 oz. of gold. But these are not worth particularizing; for they 

 all bore hammering, and flatting by rollers, to the thinness of stiff paper, and 

 afterwards working into watch-cases, cane-heads, &c. with great ease. They 

 all, indeed, became more hard and harsh, in proportion to the quantity of alloy; 

 but not one of them had the appearance of what all workmen well know by the 

 name of brittle gold. Whence it should seem, that neither tin in substance, 

 nor the fumes of it, tend much to render gold unmanufacturable. Whenever 

 therefore brittleness has followed the adding small quantities of tin to fine gold, 

 it must be supposed to have arisen from some unfriendly mixture in the tin, 

 probably from arsenic ; for other experiments have shown me, that 1 2 grs. of 

 regulus of arsenic, injected into as many oz. of fine gold, will render it totally 

 unmalleable. From the foregoing experiments I presume we may fairly con- 

 clude, that though tin, like other inferior metals, will contaminate gold, in pro- 

 portion to the quantity mixed with it, yet there does not appear any thing in it 

 specifically inimical to this precious metal. And this being contrary to the doc- 

 trine of most chemical writers, I submit whether it may not be useful to publish 

 these experiments, by laying them before the r. s. 



