179 
OF GOLD (AOT) OTHEE METALS) TO LIGHT. 
separated by the thickness of a card, and fastened at the edges by varnish internally and 
gum externally. These being filled with dense ruby or blue fluid, gave no indication of 
action on the ray, showing that the difiused particles were inoperative. The same fiuids,_ 
dried on plates of glass so as to leave films, did act just as the gold deflagrations had 
done ; 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 hght 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 extent. In this case the gold is not in one plane, but dif- 
fused through the dry jelly, and the effect is the same as if it were difiused 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 depo- 
larized the ray, required direct rotation of the analyser to attain a minimum, therefore 
rotated the plane of polarization ; but did not present sensible colour on either side of 
the minimum of light. Palladium 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 manner. These films appear to be exceedingly continuous, and it 
could be obsert^ed 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 brilliancy 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 essential to then: good action. Bhodiumfllms by phosphorus gave 
good actions, like those produced by gold. Silver deflagrations^ either in air or hydrogen, 
gave depolarizing results hke 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 
deflagi’ated in hydrogen : depolarized, bringing in a red image, which by direct rotation 
of the analyser was lowered 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 httle direct rotation of the analyser was required to produce the mini- 
mum of light. Tin deflagrated in hydrogen : depolarized and rotated the ray, as with 
gold ; the images were only feeble in colour. Lead deflagrated in hydrogen : acted as tin. 
Ii'on deflagrated in hydrogen : acted as tin. Zinc deflagrated in hydrogen : acted as tin. 
Aluminium deflagrated in hydrogen : had like action with the rest ; the image brought 
in by it was red, which direct revolution of the analyser reduced at a little distance to 
a minimum and then converted to blue. A film of mercury produced by sublimation, 
a film of arsenic produced in like manner, and a film of smoke from a candle, though 
all of them sufficiently pervious to light, did not produce any result of depolariza- 
2 B 2 
