376 
The Action of Resin and Allied Bodies on a Photographic Plate 
an the Dark. 
By WiuuiAm J. RUSSELL, Ph.D., F.RS. 
(Received March 24,—Read May 7, 1908.) 
[PLates 10—12.] 
In former papers it has been shown that certain metals, woods, juices of 
plants, etc., have the property of acting on a photographic plate in the dark ; 
that a similar action is exerted by coal resins and allied bodies is proved by 
the following experiments. 
Ordinary resin or colophony is the solid, remaining on the distillation 
of crude turpentine, and the substance known in commerce as “ amber resin” 
is ordinary resin slightly purified, and is of a lighter colour. 
To prove the activity of these bodies it is only necessary to lay them on 
a photographic plate in the dark, and afterwards to develop the plate in 
the ordinary way. The plates used in the following experiments were in 
almost all cases “ Imperial Special Rapid.” At ordinary temperatures the 
action is but slow: the contact of resin and plate would have to be for two 
to three days in order to obtain a fairly good picture. The amber resin is, 
however, slightly more active than the ordinary resin. If the temperature 
be raised, and contact be at 30° to 40° C., the action is much more rapid, 
and three to four hours is long enough to give a good picture. In fact, 
in four hours, ordinary resin will give as much action at 40° as it would in 
three days at 15° to 20°. A still higher temperature cannot be used 
with safety, for then the resin softens and adheres to the photographic film. 
Absolute contact between resin and photographic plate is not necessary, 
for if the plate be held above the resin the action still takes place, and 
will, in fact, pass through a considerable distance. In one case when 
powdered resin was placed at the bottom of a glass cylinder and the photo 
plate on the top at a distance of 120 mm., and in another case when the 
distance was 210 mm., in both cases after 18 hours’ exposure at a tem- 
perature of 40°, a dark picture was produced. Another experiment which 
shows this action of resin was made by filling a glass tube, 1 inch in diameter 
and 10 inches long, and slightly contracted at one end with small pieces of 
resin, the tube being held in a horizontal position, and a photo plate placed 
vertically at 1 mm. from the open end of the tube. On passing a slow 
current of air through the tube, which was maintained at 40° C., a dark 
