of Gold and other Metals to Light. 525 
thin feebly reflecting surface remained between it and them. 
Using alcohol, the parts already dry remained violet, when 
wetted by it; but wetting other parts with alcohol before they 
were dry from water they remained rosy, became bluish when 
ory from the alcohol, and became rosy again when re-wetted 
y it. 
It will be necessary to speak briefly of the reduction of gold 
into a divided state by some other chemical agents than those 
already described*. If a drop of solution of protosulphate of 
iron be introduced to, and instantly agitated with, a weak neu- 
tral solution of chloride of gold in such proportion that the latter 
shall be in excess, the fluid becomes of a blue-gray colour by 
transmission and brown by reflexion ; and a deposit is formed of 
a green colour by transmitted light, greatly resembling the colour 
of beaten or pressed metal. It is not however pure gold, but an 
association of it and oxide of iron. Hydrochloric or other acids 
remove the iron and reduce the gold to a dark, dense, insoluble 
set of particles, in very small quantity apparently, yet containing 
all that was present in the bulky green deposit. If the solution 
of gold be made slightly acid beforehand, then the change and 
precipitation is to appearance much less; the reflexion by the 
particles is feeble but of a pale-brown colour, the general trans- 
mitted light is amethystine; in the dark tube the tint is blue; 
the particles are much condensed and settle quickly, but occa- 
sionally leave a good ruby film on the side of the glass, which 
has all the characters of the ruby films and particles before 
described. The loose gold particles quickly adhere together. 
Hence it appears that the green precipitate often obtained by 
protosulphate of iron is not pure gold in a divided state; and 
that when care is taken to produce such pure divided gold, it 
presents the appearances of divided gold obtained by other 
means, the gold being competent to produce the ruby, ame- 
thystine, and blue colours by transmission. Usually the gold 
rapidly contracts and becomes almost insensible, and yet the 
test of protochloride of tin will show that a// has been separated 
from solution; it then forms a striking contrast to the depth of 
colour presented by the same solution of gold precipitated by 
phosphorus, and most impressively directs attention to the mole- 
cular condition of the metal in the latter state. 
A very small quantity of protochloride of tin, added to a dilute 
solution of gold, gave, first the ruby fluid, showing diffused par- 
ticles by the cone of rays; this gradually became purple, and if 
the gold were in sufficient quantity, a precipitate soon began to 
fall, being the purple of Cassius. If the chloride of tin were in 
* See Gmelin’s ‘Chemistry,’ vol. vi. p. 219, “'Terchloride of gold,” for 
numerous references in relation to changes of these kinds. 
