of Gold and other Metals to Light. 413 
pressure tended to change the blue-gray to brown. Palladium : 
the reflexion fine metallic and dark gray ; the transmitted light, 
where most abundant, sepia-brown; agate pressure converted 
the tint in the thinner places from brown towards blue-gray. 
Platinum: the reflexion white, bright and metallic; the trans- 
mission brown or warm gray with no other colours; agate pres- 
sure increased the reflexion and diminished the transmission as 
with tin. Aluminium: the reflexion metallic and white, very 
beautiful ; the transmitted light was dark brown, bluish-brown, 
and occasionally in the thinner parts orange; agate pressure 
caused but little change. 
Films of Gold (and other metals) by Phosphorus, Hydrogen, &ce.— 
effect of heat—pressure. 
The reduction of gold from its solution by phosphorus is well 
known. If fifteen or twenty drops of a strong solution of gold, 
equal to about 14 grain of metal, be added to two or three pints 
of water, contained in a large capsule or dish, if four or five 
minute particles of phosphorus be scattered over the surface, and 
the whole be covered and left in quietness for twenty-four or 
thirty-six hours, then the surface will be found covered with a 
pellicle of gold, thicker at the parts near the pieces of phosphorus, 
and possessing there the full metallic golden reflective power of 
the metal; but passing by gradation into parts, further from the 
phosphorus, where the film will be scarcely sensible except upon 
close inspection. If plates of glass be introduced into the fluid 
under the pellicle, and raised gradually, the pellicle will be raised 
on them; it may then be deposited on the surface of pure di- 
stilled water to wash it; may be raised again on the glass; the 
water allowed to drain away, and the whole suffered to dry. In 
this way the pellicle remains attached to the glass, and is in a 
very convenient condition for preservation and examination. 
If phosphorus be dissolved in two or three times its bulk of 
sulphide of carbon, and a few drops of the fluid be placed on the 
bottom of a dry basin, vapour of the phosphorus will soon rise 
up and bring the atmosphere in the basin to a reducing state. 
If a plate of glass large enough to cover the basin have six or 
eight drops of a strong neutral solution of chloride of gold 
placed on it, and this be spread about by a glass stirrer, so as to 
form a flowing layer on the surface, the glass may then be in- 
verted and placed over the dish. So arranged the gold solution 
will keep its place, but will have a film of metal reduced on its 
under surface. The plate being taken off after twenty, thirty, 
or forty minutes, and turned with the gold solution upwards, 
may then gradually be depressed in an inclined position into a 
large basin of pure water, one edge entering first, and the gold 
