464 Mr. G. Matthey. On the Preparation of the [Apr. 3, 



benefit of the excellent and valued advice of M. Stas, the celebrated 

 Belgian chemist, to all of whom the scientific world owe so much, and 

 to whom I desire to offer my warmest thanks. 



In a paper of this kind it would be superfluous for me to enter into 

 any of the already published details concerning the existence and 

 collection of what is known as platinum-dust or mineral. It is suffi- 

 cient for me to observe that the six metals (of which platinum is the 

 chief) usually found more or less in association in their native state, 

 present characteristics of interest beyond their metallurgical utility, 

 which are, perhaps, worth alluding to en passant. It is, for 

 instance, a curious fact that the group should consist of three light 

 and three heavy metals, each division being of approximately the 

 same specific gravity — the heavier being (in round figures) just double 

 the density of the lighter series. 



Thus we find osmium, iridium, platinum forming the first division, 

 of the respective specific gravities of 22*43, 22*39, 21*46 ; whilst 

 ruthenium, rhodium, and palladium are represented by the figures 

 11'40, 11*36, 11, the average densities of the heavy and light divisions 

 thus being respectively 22*43 and 11/25. 



But a more interesting and important classification is what I may 

 designate as a first and second class series, from the more important 

 view of their relative properties of stability. Thus platinum, palla- 

 dium, and rhodium form the first or higher class, not being volatiliz- 

 able in a state of oxide ; iridium, osmium, and ruthenium forming tbe 

 second or lower class, their oxides being more or less readily volati- 

 lized. 



The oxide of iridium is affected at 700 to 800° C, and entirely decom- 

 posed at 1.000°, whilst osmic and hyporuthenic acids are volatilized at 

 the low degree of 100°, the latter exploding at 108°. The chlorides 

 of these metals can be sublimed at different temperatures (as also the 

 protochloride of platinum). 



I now propose to give a short description of the methods I have 

 employed for preparing the pure platinum and iridium necessary for 

 the manufacture of the alloy, which I call " iridio-platinum," and it 

 is upon the distinguishing characteristics above-mentioned that my 

 method of separation is chiefly founded. 



Platinum. 



The preparation of this metal to a state of purity is an operation 

 of extreme delicacy. I commence by taking ordinary commercial 

 platinum ; I melt this with six times its weight of lead of ascertained 

 purity, and, after granulation, dissolve slowly in nitric acid diluted in 

 tne proportion of 1 volume to 8 of distilled water. The more readily to 

 ensure dissolution, it is well to place the granulated alloy in porcelain 



