of Gold and other Metals to Light. 537 
for though the particles were very irregularly spread, parts of 
the general deposit, and these not the thickest, could be selected, 
which produced the effect excellently well. 
When the coloured jellies are laid upon glass plates and 
allowed to dry, the plates introduced obliquely into the sulphide 
of carbon affect the ray, but not as gold films; the light image 
becomes visible, but the plane of polarization is not changed ; 
the light is coloured by the ruby or blue tint of the gold present, 
but a film of jelly without gold makes it visible to the same ex- 
tent. In this case the gold is not in one plane, but diffused 
through the dry jelly, and the effect is the same as if it were 
diffused through water, being negative. 
Such are the effects with the various preparations of divided 
gold. I will hastily notice what occurs with some other metals. 
Platinum deflagrated in hydrogen: it depolarized the ray, re- 
quired direct rotation of the analyser to attain a minimum, there- 
fore rotated the plane of polarization; but did not present 
sensible colour on either side of the minimum of light. Padlla- 
dium deflagrated in hydrogen: it depolarized, producing a red 
image ; direct rotation of the analyser lessened the light to a 
minimum, and then brought in a blue image. The films of 
palladium obtained by phosphorus acted well in the same man- 
ner. These films appear to be exceedingly continuous, and it 
could be observed in them, that though the thickest were not 
the best, yet films could be obtained so thin as to be distinctly 
inferior to other parts a little thicker ; also that where the bril- 
liancy of reflexion which indicates perfect smoothness passed in 
any degree into dulness, the action of the film was injured: the 
perfect condition of the surfaces of the films seems to be essen- 
tial to their good action. Rhodium films by phosphorus gave 
good actions, like those produced by gold. Stlver deflagrations, 
either in air or hydrogen, gave depolarizing results like those 
with gold. Silver films also gave excellent results of the hke 
kind. A thin pale-brown film was much better than a thicker 
one. Copper deflagrated in hydrogen: depolarized, bringing in 
ared image, which by direct rotation of the analyser was Jowered 
a little and then converted to blue. The copper films obtained 
from oil acted in the same manner; the red and blue images 
appeared in their order; but very little direct rotation of the 
analyser was required to produce the minimum of light. Tin 
deflagrated in hydrogen: depolarized and rotated the ray, as 
with gold; the images were only feeble in colour. Lead defla- 
grated in hydrogen : acted astin. Jron deflagrated in hydrogen : 
acted as tin. Zinc deflagrated in hydrogen: acted as tin. Alu- 
minium deflagrated in hydrogen : had like action with the rest ; 
the image brought in by it was red, which direct revolution of 
