95 
Wood on Photographic Plates. 
They were exposed at 40° C. for 120 hours. In every case a good negative 
was obtained. It would appear that steaming has the effect of diminishing 
the activity of the wood on a photographic plate for a time only and not 
permanently. This method is, therefore, useless for detecting artificial 
seasoning or drastic treatment with wet or dry heat. 
III. The Identification of Timbers. 
Russell said in his papers that Scotch Pine in the dark acts on a photo- 
graphic plate in such a way that the spring wood gives a dark ring and the 
summer or autumn wood does not have any effect. So the plate shows 
a dark ring for every ring of spring wood and a light one for every ring of 
autumn wood (Fig. 2). He stated that all the Pines he tested behaved in 
the same way. On the other hand, Larch gives a reverse image, the spring 
wood being negative and the autumn wood positive (Fig. 3). It seemed 
that this method would provide a means of distinguishing between a Pine 
and a Larch. 
In the course of 'my preliminary experiments with Scotch Pine, to 
determine time of exposure and optimum temperature, I came across 
a specimen of Scotch Pine that gave the reverse image ; its spring wood 
was negative and autumn wood positive, so it resembled a Larch. Struc- 
tural examination confirmed that it was Scotch Pine. It was then necessary 
to ascertain the action on a photographic plate in the dark of a number of 
different specimens of Scotch Pine, under varying conditions, to see if there 
were other exceptions. Also it was considered that there might be some 
difference in behaviour of heart-wood and sap-wood, so in the specimens 
selected for experiment some were pure sap-wood, some pure heart-wood, and 
some partly one and partly the other. In each case the history of the 
particular Scotch Pine was known and two pieces of wood were selected 
from each specimen. One piece was air-dried, so it was left in moist air 
before the experiment was performed ; the other had been dried at ioo° C. 
for two days. 
The following results were obtained : 
No. of 
No. of 
Condition 
Temp, and Time 
Type of Wood. 
Spring 
Autumn 
kjCUI Lrl> 
Pine. 
Plate. 
of Wood. 
of Exposure. 
Wood. 
Wood. 
321 
Fig. 4 
5 2 
Moist air 3 days 
% 
O 
24 hrs. 
Sap-wood chang- 
ing to heart- 
wood 
+ 
- 
56 
Dried at 1 oo° C. 
>> 
99 
Do. 
+ 
_ 
100 
Do. 
27 0 C. 
72 hrs. 
Do. 
+ 
— 
IT 4 
Moist air 3 days 
4 o°C. 
2 4 „ 
Do. 
+ 
— 
321 
Do. 
99 
4 ^ >j 
Do. 
+ 
— 
1 31 
Dried at ioo° C. 
9 9 
96 „ 
Do. 
+ 
— 
147 
Moist air 1 day 
99 
48 „ 
Do. 
+ 
— 
191 
Steamed 1 2 hrs. 
and left 41 days 
99 
120 „ 
Do. 
+ 
“ 
