Composition of Brittle Platinum. 85 



analysis. It was decided to rely upon the spectrograph!© 

 method, but considerable difficulties were encountered in 

 operating- on fragments of metal of such very small dimensions 

 that it was almost impossible to make use of any form of clip 

 to hold them in. Between thirty and forty photographs of 

 spark -spectra were obtained and carefully examined. 



It was proved beyond doubt that the following metals were 

 most certainly completely absent, namely : — zinc, cadmium, 

 copper, silver, mercury, tin, lead, arsenic, antimony, bismuth, 

 tellurium, nickel, cobalt, aluminium, gold, chromium, and also 

 the metals which would scarcely be expected to be found in 

 platinum, namely indium and thallium. In no case could there 

 have been l/10thof a per cent, present, and in some instances 

 even 1 /1000th of a per cent, was excluded. A very careful 

 examination was made for iron as this element is difficult to 

 remove entirely from platinum, and for this purpose a 

 spectrum of the purest platinum obtainable from Messrs. 

 Johnson and Matthey was photographed. The photographs 

 were also compared with those of the iron-spectrum and the 

 platinum-spectrum published in the Trans. Chem. Soc. 1882. 

 It was found that the pure platinum electrodes o-ave spectra 

 identical line for line with the spectrum of two fragments of 

 brittle platinum. It was therefore concluded that any 

 metallic impurity in the brittle platinum must be in so very 

 minute a proportion that it was impossible for it to impair its 

 toughness. It was thought that the platinum might perhaps 

 contain iridium, but a comparison of the platinum-spectrum 

 with that of iridium showed that the strong lines of the latter 

 element were absent from the platinum. There remain now 

 certain non-metallic elements such as phosphorus, carbon, 

 and silicon to be considered as possible impurities. In the 

 United States, phosphorus has been added to native iridio- 

 platinum for the purpose of rendering it fusible. It is said 

 that the phosphorus is entirely eliminated from the iridio- 

 platinum alloys by long continued heating. There appears to 

 be no possibility of more than a very minute trace of iridium 

 in the metal and the brittleness is not caused by that because, 

 if it were, melting would not improve its malleability. Proof 

 of melting having this effect occurs later. 



It is, however, very possible that phosphorus may be 

 present, and as the effect of phosphorus in minute proportions 

 is to render platinum brittle and crystalline, the properties 

 seen in the pins from this point of view are quite what might 

 be expected and even predicted. Phosphorus would not be 

 detected by the method of spectrum analysis, and it is 

 extremely doubtful if any chemical method of separation 



