1825,] anAtihi/ofGoldandiihodium.^ SS8 



it have contained a larger quantity of gold? I should be the 

 more inclined to think so, because, from the fourth part of the 

 same solution, precipitated by ammonia, which should have 

 contained 16*5 grains of alloy, I obtained only 9-3 of gold ; 

 which gives 43 per cent, of rhodium in the alloy. The remain-*, 

 ing solution had the colour of protosuJphate of iron. 



5. In this state of things, Citizen Mendez conceived the ideat 

 of adding sulphuric acid to a solution of 10 grains of another 

 alloy (specific gravity = 16*8) in aqua regia, and distiUing it to 

 dryness. When all the muriatic acid had come over, and the 

 liquid in the retort had assumed a very deep red colour, the 

 receiver was changed ; a yellow matter rose with tlie acid, and 

 the gold remaining in the retort, had the appearance of aurum 

 musivum. The yellow matter partly dissolved in water, colour- 

 ing it first yellow, afterwards green, and a sub-trito-sulphate of 

 rhodium, of a yellow ochre colour, deposited. On pouring 

 water into the retort, a similar deposit was obtained, which was 

 separated by decantation ; the gold was then twice fused with 

 potash and nitre ; after the first fusion it left a very dark leek- 

 green glass, and a brighter one after the second ; so that it 

 would be necessary to repeat the operation several times to 

 obtain the gold perfectly pure ; it -weighed in the state in which 

 we left it, 8*2 grains. We see, therefore, from what has been 

 said, that rhodmm alloys with gold in different proportions, the 

 mean, according to what I have observed, being 34 of rhodiun^ 

 in 100 parts of the alloy ; or more than one third. 



I am sorry to be compelled to say that Dr. Wollaston is mis- 

 taken, in stating that the alloys of gold with rhodium are very 

 ductile. The contrary has long been observed at this Parting 

 House, and was attributed to the sharpness of the acids {acrete 

 des acides), as if we employed more than one, and they were 

 very volatile, and very easily decomposed. We can now con- 

 ceive that a brittle metal in so large a quantity must necessarily 

 render the alloys it forms brittle also. 



I imagine our practical men will not any longer assert, that 

 with a cupel, and Hvo. or three acids, any fraudulent mixture may 

 he detected in gold, now that they have this new instance of rho- 

 dium, in addition to those known before, of platina and palla- 

 dium, and I hope that iridium will also some day play its part. 

 As to the enormous losses at the Parting House, 1 understand 

 that in former times long reports have been made concernino* 

 them, but experiment is the right method of discovering phy- 

 sical truths. The reports are like Spartan money, far greater in 

 volume than in value, 



I do not believe that the complete separation of rhodium can 

 be effected by softening (adoucissant) the alloy with corrosive 

 sublimate, although this method be more chemical than that 6f 



