DR. W GEOFFREY DUFFIELD ON THE 



for 



<* to deterge Aether the tota, intensity of 

 a hr function of the pressure, though, with the exception of the 

 5 to 20 .Spheres, the brightness appeared to mcrease stead.ly as the 



pressure was increased. .. 



(4) A Chang* in the Physical Properties of the Gold.-A source of great trouble 

 was the melting of the lower pole, which was so rapid that when the pressure 

 cylinder was opened after the first set of 12 photographs had been taken, only T mch 

 of the original l inches of this pole remained, the rest of the metal having trickled 

 down the sides and solidified in ridges and lumps, exactly like the wax of a candle 

 that has burned rapidly in a gust of wind. The other pole had remained intact. 



The obvious course was to interchange the poles, first paring the drippings from 

 what had previously been the lower one. With this re-arrangement a second set, 

 comprising 14 photographs, was taken, and the conditions were, as far as the writer is 

 aware, exactly the same as those under which the first set was obtained, and the 

 pressures were extended over the same range of 1 to 200 atmospheres. Less diffi- 

 culty was experienced from the irregular burning of the arc, and its image could 

 always be easily guided by the mirror system upon the slit of the spectroscope. 



At the end of these experiments it was expected that the lower pole would be 

 found to have melted away as before ; but this was not the case, it was as little 

 affected as when it had served as the top electrode, its upper surface being but 

 slightly pitted. Nor did a subsequent set of 8 photographs at the same pressures 

 cause either pole to melt. 



A physical change had been accomplished in the gold whereby it no longer melted, 

 though placed under conditions under which a similar rod of gold had previously 

 melted freely. 



It is quite possible that the raising of the melting-point is due to a direct effect of 

 pressure upon the metal, though we must also consider as possible factors the passage 

 of a current of 10 to 15 amperes through the rod, a repeated annealing action, and 

 perhaps some absorbent action by the hot poles of the gases within the cylinder 

 which might affect their properties, though this last action might have equally well 

 taken place during the original refining of the metal. 



(5) The Occurrence of the Calcium Lines H and K. In spite of the fact that the 

 spectrum of gold did not when first examined show any impurity, either recognised 

 or suspected, very abundant evidence of the presence of calcium is presented by the 

 photograph taken at a pressure of 10 atmospheres in the region X 3550 to A. 4000 

 (Plate 2) upon which the H and K lines appear more strongly than any other line, 

 being very much more prominent than the gold line /2 at 3898*04. This is the more 



