6 
Transactions of the Society. 
of silver cupel! ation bead when present up to 2 p.c., as far as can 
be ascertained by the naked eye, but when examined under the 
microscope such beads present an appearance similar to that 
produced by platinum. The effect of palladium on gold and gold- 
silver beads has not yet been studied seriously. 
Iridium does not appear to alloy with silver at the temperature 
of cupellation, but owing to its density sinks towards the bottom 
of the button whilst the latter is in the fluid condition. It has been 
found, however, that these beads are much more spherical on the 
upper and lower surfaces, giving to them the appearance of having 
been expanded by an internal pressure. Micro-examination shows 
that the crystals are well defined, but the facets are striated, or 
marked with a series of lines crossing one another after the manner 
of slip-bands. These markings would seem to confirm the sugges- 
tion just made that the beads have been subjected to severe internal 
stresses, and this is supported by the fact that in a large number 
of silver-iridium beads a cavity or cavities can be found not far 
distant from the upper and lower surface. Fig. 5, obtained from 
the section of a bead containing 2 p.c. iridium, shows the particles 
near the base of the bead and the cavities to which reference has 
been made. 
Small quantities of rhodium have a very marked effect on 
silver beads, 0*03 to 0*04 p.c. producing a bluish grey colour due 
to a film of rhodium or a rhodium compound. With smaller 
quantities of rhodium, such as 0* 01 p.c., the beads are silver white, 
but a distinct crystallization is set up visible to the naked eye, 
and so distinct as to give the appearance of a cut gem, as seen in 
fig. 6. 
It may be contended that surface appearances are not to be 
relied upon, as many factors may influence the result. It should 
be remembered, however, that cupellation must be carried out as 
far as possible under standard conditions, and therefore what may 
apply in the case of other metals does not apply in the phenomena 
now being considered. The author is continuing this work by en- 
deavouring to ascertain if there is any relation between the internal 
structure as revealed by polished and etched sections and the surface 
EXPLANATION OF PLATE II. 
Fig. 7. — Silver + 1*4 p.c. platinum. Section, x 100. 
Fig. 8. — Silver + 3 p.c. palladium. Section, x 100. 
Fig. 9. — Manganese bronze, x 100. 
Fig. 10. — Manganese bronze, x 100. 
Fig. 11. — Manganese bronze, x 100. 
Fig. 12. — Silver-copper eutectic. 
Tbe magnification as given refers to the original photomicrographs. The 
illustrations have been reduced and are at a magnification equal to ^ths of the 
figures given. 
