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or GOLD (AOT) OTHEE METALS) TO LIGHT. 
Films of Gold [and other metals) hy Phosphorus, Hydrogen, &c. — 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 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 metalhc 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 distilled water to wash it ; may be raised again on the glass ; the 
water allowed to drain away, and the whole sufiered 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 inverted 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 tmaied with the gold solution upwards, may then gradually be depressed 
in an inchned position into a large basin of pure water, one edge entering first, and the 
gold film will be left floating. After sufficient washing it may be taken up in portions 
on smaller plates of glass, dried, and kept for use. Mr. Warren De la Eue taught me 
how to make and deal with these films : they may by attention be obtained very uniform, 
of very different degrees of thickness, from almost perfect transparency to complete 
opacity, and by successive application of the same collecting glass plate may be super- 
posed with great facihty. 
These films may be examined either on the water or on the glass. When thick, their 
reflective power is as a gold plate, full and metallic; as they are thinner they lose reflect- 
ive power, and they may be obtained so thin as to present no metallic appearance, all 
the coloured rays of light then passing freely through them. As to the transmitted 
light, the thinner films generally present one kind of colour ; it appears as a feeble grey- 
violet, which increases in character as the film becomes thicker and sometimes approaches 
a violet ; a greenish violet also appears ; and the likeness of the grey-violet tint of these 
films to the stains produced by a solution of gold on the skin or other organic reducing 
substance, or the stain produced on common pottery, cannot be mistaken. Superposition 
Y 2 
