156 
DE. EAEADAT 01s THE EXPEEDm'TAL EELATIOXS 
of several grey-violet films does not produce a green tint, but only a diminution of Hgbt 
without change of colour. In those specimens made by particles of phosphorus 
floating on the solution of gold, very fine green tints occur at the thicker and golden 
parts of the film. The colour of the gold here may depend in some degree on the 
manner in which these films are formed : the thicker parts are not produced altogether 
by the successive addition of reduced gold from the portion of fluid immediately beneath 
them. When a particle of phosphorus is placed on pure water, it immediately throws 
out a film which appears to cover the whole of the surface ; in a little while the film 
thickens around the particle and is easily distinguished by its high reflective power. It 
is this film which reduces the gold in solution, being itself consumed in the action ; the 
result is a continued extension from the phosphorus outwards, which, after it has covered 
the solution with a thin film of gold, continues to cause a compression of the parts aroimd 
the phosphorus and an accumulation there, rendering the gold at a distance of half an 
inch from the phosphorus so thick, that it is brilhant by reflexion and nearly opake by 
transmission, whilst near to the phosphorus the forming film is so thin as to be observed 
only on careful examination, and is still travelhng outwards and compressing the 
surrounding parts more and more. The phosphorus is very slowly consumed ; a particle 
not weighing y^th of a grain will remain for four or five days on the surface of water 
before it disappears. 
Though the particles of these films adhere together strongly, as may be seen by their 
stifihess on water, still the films cannot be considered as continuous. If they were, those 
made by vapour of phosphorus could not thicken during their formation, neither could 
they dry on glass in the short time found sufficient for that purpose. Experimentally 
also, I find that vapours and gases can pass through them. Very thin films without 
folds did not sensibly conduct the electricity of a single pair of Geove’s plates ; thicker 
films did conduct ; yet with these proofs that these films could not be considered as con- 
tinuous, they acted as thin plates upon light, producing the concentric lings of coloiu's 
round the phosphorus at their first formation, though their thickness then could scarcely 
be the y^th, perhaps not the of ^ wave undulation of light. Platinum, palladium, 
and rhodium produced films, showing these concentric rings very well. 
Many of these films of gold, both thick and thin, which being of a grey colour ori- 
ginally, were laid on a solution of cyanide of potassium to dissolve slowly, changed colour 
as they dissolved and became green ; if change occurred, it was always towards green. 
On the other hand, when laid on a solution of chlorine, the change during solution was 
towards an amethyst or ruby tint. The films were not acted upon by pm-e nitric, or 
hydrochloric, or sulphuric acids, or solutions of potassa or brine. They dissolved in damp 
chlorine gas, not changing in colour during the solution. I believe them to consist of 
pure gold. 
When these gold films were heated to dull redness they changed. The reflexion, 
though not much altered, was a little more metallic and golden than before ; more hght 
was transmitted after the heating and the colour had altered from greenish to riolet, or 
