THE ORIGIN OF MOSS GOLD. 291 
arsenic filled in to about one inch, then a plug of asbestos and 
upon this the spirals of gold foil were placed, the tube was held in 
an inclined position in a retort stand and the arsenic volatilized 
by a bunsen flame, when the air had been displaced by the arsenic 
vapour the gold was heated to redness by the blowpipe; it quickly 
began to fuse and to run down upon the asbestos. (The blowpipe 
flame was quite incapable of fusing the gold by itself in the tube, 
even when the blast was kept up for an hour or so and the tube 
softened out of shape, but in the arsenic vapour the gold ran down 
with great readiness at a dull red heat.) The compound of gold 
and arsenic formed is very fusible and remains liquid for some 
little time after removal from the flame and when it has much 
cooled down ; the globules are large and much rounded so that its 
Surface tension is great, like that of the liquid alloy of potassium 
and sodium, in fact the appearance of the fluid arsenide reminded 
me very much of that alloy, except that the arsenide is ofa 
yellow colour. 
The gold arsenide solidifies suddenly on cooling (superfusion) 
and sometimes spirts a good deal, the small projected globules 
attach themselves to the glass tube, but can be readily removed. 
The cooled mass is often coarsely crystallized on the surface, 
when it presents a bright lustrous gold colour and appearance, but 
underneath it is seen to be honeycombed in every direction. In 
the cavities the microscope shows spirals and spiculee of gold or 
of the gold-like arsenide. It is very brittle and breaks readily ; 
inside it is crystalline and may be cavernous, in places there are 
patches of a bright metallic grey colour. This may be due to 
the presence of free arsenic or to a grey alloy, but I have not yet 
had time to determine this. In other cases the resulting com- 
pound has the dull ochre colour of moss of precipitated gold. 
The alloy first formed by simple fusion seems to greedily absorb 
more arsenic, 2.¢., when a piece of arsenic is pushed up against it; 
the alloy wets the arsenic and on slowly withdrawing the arsenic 
the alloy follows it like a streak of water, for from one quarter 
to half an inch. The apparent absorption of the arsenic may be 
