416 Prof. Faraday on the Experimental Relations 
no such evident appearance in these cases, as in the unattached 
gold-leaf of the particles running up into globules. 
A given film, examined very carefully in the microscope by 
transmitted lamp-light, with an aperture of 90° and power of 700 
linear, presented the following appearances. The unheated part 
was of a gray colour, and by careful observation was seen to be 
slightly granular. By very close observation this gray part was 
often resolvable into a mixture of green and amethystine striz, 
it being the compound effect of these which in general produces 
the gray sensation in the eye. When a part of such a film was 
heated, the transmitted colour was changed from gray to purple, 
as before described, and the part thus heated was evidently more 
granular than before. This difference was confirmed in other 
cases. That the heated part should thus run up, seems to show 
that many of the particles must have been touching though they 
did not form a continuous film ; and on the other hand, the dif- 
ference between the effect here and with unattached gold-leaf, 
shows that the degree of continuity asa film must be very small. 
When these heated films were greened by agate pressure, or the 
drawing pressure of a card, the green parts remain granulated, 
apparently in the same degree as when purple. The green was not 
subjective or an effect of interference, but a positive colour belong! 
ing to the gold in that condition. Every touch of the agate was 
beautifully distinct as a written mark. The parts thus greened 
and the purple parts appeared to transmit about the same amount 
of light. Though the film appeared granulated, no impression was 
made upon the mind that the individual particles of which the 
film consisted were in any degree rendered sensible to the eye. ~ 
The unheated gold films when pressed by agate often indicated 
an improved reflective power, and the light transmitted was also 
modified ; generally it was less, and occasionally tended towards 
a green tint; but the effect of pressure was by no means so evi- 
dent as in particles which had been heated. 
Films of some other metals were reduced by phosphorus in 
like manner, the results im all these cases being of course much 
affected by the strength of the solution and the time of action ; 
they are briefly as follows. Palladium: a weak solution of the 
chloride gave fine films, apparently very continuous and stiff; 
the reflexion was strong and metallic, of a dark gray colour; the 
transmission presented every shade of Indian ink. Platinum 
chloride gave traces of a film excessively thin, and very slow in 
formation. Rhodium chloride in three or four hours gave a 
beautiful film of metal in concentric rings, varying in reflecting 
and transmitting power over light and also in colour; those 
which reflected well, transmitted little light; and those which 
transmitted, reflected little light ; one might have thought there 
