180 
DE. FAEADAT ON THE EXPEEDJENTAE EELATIONS 
tion. Filins of the smoke of burning zinc^ of antimony^ or of oxide of iron produced 
no effect. 
, I placed some metallic solutions in a weak atmosphere of sulphuretted hydrogen. 
Gold and platinum gave no films ; silver so poor a film as to be of no use ; and lead 
one so brittle as to be unserviceable. That obtained with palladium I bebeve to be the 
metal itself. The films of sulphuret of mercury, sulpburet of antimony which was 
orange, and sulphuret of copper which was pale brown, all acted on the hght and depo- 
larized it. The sulphuret of copper presented a difference from the metals generally, 
worth recording ; it depolarized the light, producing an image which, if not blue at once, 
was rendered blue by a httle direct rotation of the analyser ; after which the same motion 
brought in a minimum and then produced an orange or red tint, i. e. with the sul- 
phuret of copper the warm and cold tints appear on opposite sides of the minimum to 
those where they occur when films of the metals are employed, though the minimum in 
both cases is in the same direction. 
Many of the results obtained in the sulphide of carbon were produced also in cam- 
phine, the analyser being in each case adjusted to the minimum of light before the 
metallic plate or film was introduced. I pass, however, to a very brief account of some 
polarizations effected by the metals themselves in the sulphide of carbon, in which case 
the polarizing Nicol prism was dispensed with. The results show that all the dry 
forms of gold accord in giving the same manifestation of action on hght, whatever the 
state of their division, provided they be disposed in a thin regular layer, equivalent to 
a continuous film. It was first ascertained that a plate of crown-glass in an inclined 
position in sulphide of carbon gave no signs of polarity to a ray of light passing through 
it. When fine gold-leaf was on the glass and inclined to the ray, it polarized the hght, 
and exactly in the same manner and direction as a bundle of glass plates in the same 
position in the air. More hght passed than when the gold-leaf was in ah, but it could 
not be so completely polarized ; the minimum hght was of a pale bliush coloiu’. A 
thinned gold-leaf produced the same effect, but let more common hght through. I 
think the difference between gold-leaf and sulphide of carbon is sensibly less than that 
between the metal and ah. The depositions of deflagrated gold, the films of gold 
obtained by phosphorus, and even the heated deflagrated gold, produced polarizing 
effects, which, though not large, were easily recognized and distinguished from the non- 
action of the glass. Gold-leaf and gold films on glass produced a hke effect in a cam- 
phine-bath, the results being easily distinguished from those of the glass and camphhie 
only, in places where the glass had been cleared from gold. 
Films of palladium, rhodium, silver, a plate udth deposited gold particles, and a layer 
of deflagrated silver particles gave a like result, the effect varying in degree. The sul- 
phuret of copper before spoken of as in contrast with the metals, gave only a doubtful 
result, if any. 
Before concluding, I may briefly describe the following negative results ufith the pre- 
parations of gold. I prepared a powerful electro-magnet, sent a polarized ray across 
