CONTROL OF DECAY IN PULP AND PULP WOOD 33 
EXPERIMENTAL PROCEDURE 
TESTS AT FOREST PRODUCTS LABORATORY 
During the course of this study, 112 different chemical preserva- 
tives were investigated, with the object of finding an efficient one 
that could be applied to pulp at a reasonable cost. 
About 3,000 small ground-wood laps and 1,400 sulphite laps were 
treated and tested under laboratory conditions, in addition to ground- 
wood pulp experimentally treated in the two mill tests described in 
the following section. 
Laboratory procedure was in general, as follows: On a small wet 
machine there were run off laps of fresh pulp about 25 inches long, 
12 to 14 inches wide, and one-eighth inch thick. After the laps had 
been trimmed to about 21 inches in length they were separated into 
bundles of 7 and 3. Each bundle was then weighed separately, and 
all 10 laps were afterwards spread out on a table and sprayed on both 
sides with preservative by means of an ordinary hand-operated 2}^- 
gallon compressed-air garden sprayer. 
Moisture determinations showed the ground-wood and sulphite 
laps to be about 30 and 25 per cent oven-dry, respectively, before 
spraying. Each piece of the lot containing seven laps was then in- 
oculated by shaking on one surface from an atomizer bottle a heavy 
water suspension of the mixed spores of 25 molds. The three other 
laps were each inoculated in 10 places with mycelial cultures of &ve 
wood-destroying fungi grown on agar, small squares of the agar 
being cut out with the growing fungus. After inoculation each lot 
of seven and of three was folded once and then weighed for the 
second time in order to determine the amount of preservative in 
the pulp, the weight of inoculating substance being negligible. 
The amount of pulp treated at the laboratory varied from 3 to 15 
pounds, oven-dry weight, for each concentration applied. The con- 
centration of solution used was to a certain extent limited by the solu- 
bility of the chemical; but where the antiseptic value was doubtful 
and the substance easily water-soluble in the desired amount, 5 per 
cent solutions were chosen for the preliminary tests. In later tests of 
substances which looked promising the concentrations, and hence the 
amount of antiseptic per unit of pulp, were in many cases reduced. 
At the end of a day's run the bundles of laps were taken to a storage 
house (PL XIII, fig. 1) in which the air was kept highly humid and the 
temperature held at 72 to 75° F. The bundles of seven laps in- 
oculated with molds were for the first few months stacked closely on 
narrow shelves, with one or more untreated laps separating the 
treated bundles, and with occasional bundles of untreated test laps 
interspersed at random to serve as checks or blanks. For the last 
10 months of the test, however, the bundles were repiled with thick 
laps of very rotten hydraulic-pressed pulp separating the layers, so 
as to give a more severe infection. The bundles of three laps, in- 
oculated only with wood-destroying fungi, were piled on other 
shelves and separated only by laps of clean, untreated pulp. 
The increase of moisture content due to treatment varied, of 
course, with the amount of solution applied, but no records of this 
were taken at the time of spraying. 
523°— 25f 3 
