370 Scientific Proceedings, Royal Dublin Society. 



distributed, alone display this lustre. The deposit is compara- 

 tively small in area. 



Lead. — Lead forms .a larger deposit, consisting entirely of 

 oxide. It is white at the outer edge, yellow and brown as it ap- 

 proaches the perforation, and at the centre occasionally vermilion- 

 red in colour. 



The lips of the perforation are quite smooth and rounded in 

 shape, never jagged, and the perforation is much larger than with 

 other metals. These effects are caused by the great fusibility of 

 the slag formed by the action of the lead oxide on the mica. In 

 every direction around the hole drops of slag are projected, and 

 are seen on the mica. 



Tin. — Tin forms a deposit of white oxide similar in size to 

 that of copper. 



Arsenic. — Arsenic forms a very large deposit of white oxide. 

 Round the perforation a brown to black deposit of the substance, 

 in an unoxidized form, is visible by transmitted light, and a small 

 ring by reflected light. 



Antimony. — Antimony forms a large deposit, smaller, how- 

 ever, than that of arsenic. It is bluish at the edges, and becomes 

 denser and whiter towards the centre ; around the perforation it is 

 yellow. It is composed entirely of oxide. 



Bismuth. — Bismuth gives a fine brown deposit, which is 

 stronger and larger than that of antimony. Its appearance is 

 very striking. No metal present. Slag is very fusible, as with lead. 



Thallium. — Thallium yields a dark-brown deposit of large size, 

 presumably all oxide. It is very striking and characteristic. 



Magnesium. — This metal yields a white deposit. 



Zinc. — The deposit of zinc is fairly large, and varying in 

 colour from white at the edges to yellow at and towards the 

 centre. Probably, if it contained no trace of cadmium, the deposit 

 would be entirely white. 



Cadmium. — Cadmium gives a fine large deposit of a rich brown 

 tint, verging on yellow, when the film is very thin. It appears to 

 be entirely composed of oxide. 



Graphite. — This substance yields a black deposit of carbon. 



Iron. — Pure iron forms a dense brown to black deposit, con- 

 fined to a small area round the perforation. In the thinnest part 

 of the film the transmitted light is reddish, varying from a chestnut- 



