CONTROL OF DECAY IN PULP AND PULP WOOD 35 
marked, and could be compensated for by slight adjustments and by 
occasional picking out. With entirely clear, carefully strained solu- 
tions probably no difficulty would be experienced. 
From 125 to 250 pounds of pulp, oven-dry weight, were treated 
with each concentration of preservative. The amount of chemical 
applied was figured on the basis of 70 per cent retention. After 
treatment, the pulp, together with a quantity of untreated material, 
was piled in the basement of the mill for later observation. 
RETENTION OF CHEMICAL ON WET MACHINE 
The amount of chemical actually retained by pulp sprayed at the 
press rolls depends mainly on the pressure applied at the rolls. To 
obtain experimental data on this question several tests involving 
somewhat more than 200 pounds of wet pulp were conducted on the 
small wet machine at the laboratory. Sodium chloride (common salt) 
was the chemical used, for the reason that it can very easily be washed 
from pulp and quantitatively determined with silver nitrate. 
The salt solution was dropped on the pulp at the press roll from a 
three-eighth-inch brass spray pipe having one sixty-fourth-inch 
perforations spaced three-fourths inch between centers. The speed 
of the sheet was 41.9 feet per minute. Every tenth lap, or approxi- 
mately one lap every five minutes, was sampled for sodium chloride 
and moisture. 
In the case of a 5 per cent solution, approximately 70 per cent of 
the dry weight of salt was retained by the pulp. With a 25 per cent 
solution, the retention was somewhat greater (74 per cent), as less 
of the solution had to be applied to leave equivalent quantities of 
dry salt in the pulp. In mill practice some of the chemical can be 
recovered by recirculation of the white water. 
DIFFUSION OF CHEMICAL IN PULP 
The rate and amount of diffusion of chemical in the pulp have an 
important bearing on the tests conducted and are of particular 
importance in determining the commercial method of applying pre- 
servatives on the wet machine. To get information on this point, a 
series of special tests with sodium chloride was begun. 
Some of the ground-wood laps used in the sodium chloride retention 
tests were reserved for the purpose, and a number of fresh laps of 
ground wood were run off at a moisture content of 71 to 73 per cent. 
In one set of tests 14 treated and 90 untreated laps were sprayed 
with filtered lake water in quantities as nearly as possible equal to 
those used in the regular preservative tests. The treated laps were 
gathered into 2 bundles of 7 and folded once; the un treated into 18 
bundles of 5 and folded once, making 10 thicknesses to a bundle. A 
"sandwich" stack was then built up of 6 untreated bundles and 1 
treated bundle alternately, 5 layers in all, each layer of treated pulp 
thus being faced with 60 thicknesses of untreated. 
In a second set of tests, 28 treated and 50 untreated laps were 
taken. Their moisture contents ranged from 71 to 73 per cent, and it 
was decided not to add water. They were folded in the same sized 
bundles as the laps used in the first test and piled together, the 
treated bundles being laid between 20-fold thicknesses of untreated 
laps. 
