142 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1953 



Treatment of the Test Blocks 



The blocks selected for any given treatment are numbered serially 

 with India ink on the upper half of one of the radial faces. All blocks 

 are then oven-dried for 24 hours at 105°G to an approximate constant 

 weight. The blocks are removed from the oven, and placed in a desiccator 

 over P2O5. Check tests of blocks held under these conditions show that 

 they do not change weight by more than one hundredth gram within 

 the period they are held for weighing. The cooled, oven-dried blocks are 

 weighed to the nearest hundredth gram. 



The weighed blocks are placed in beakers and arranged with a tan- 

 gential face down so that the transverse surfaces do not touch and the 

 holes are vertical. This refinement in placing the blocks may not be nec- 

 essary to obtain satisfactory absorption, but the procedure has worked 

 out well, and it has been followed consistently. For any given concen- 

 tration a sufficient amount of creosote, for example, and toluene are 

 combined by weight to leave in the blocks, after treatment, the desired 

 retention of preservative. Experience has indicated the concentration 

 required, which depends to a certain extent upon the type of vacuum 

 equipment that is available as well as upon the density of the blocks 

 to be treated and the nature of the treating solution. Actually the process 

 of treatment is simple. The beaker containing a given lot of weighed 

 oven-dried blocks is placed within a bell jar and subjected to a vacuum 

 of 3 to 4 millimeters of mercury. When this vacuum has been reached 

 the line to the vacuum pump is shut off, and the preservative is run into 

 the beaker from a separatory funnel^^^ fitted into a rubber stopper on 

 the top of the vacuum chamber, the blocks being weighted down below 

 the level of the preservative. 



The absorption and distribution of the oil within the blocks seems to 

 take place very rapidly. Generally speaking, the beaker containing the 

 blocks and the preservative are removed from the vacuum chamber as 

 soon as practicable to permit continuing the treatment of another group 

 of blocks. However, the blocks are usually held in the preservative solu- 

 tion for an hour or two, which apparently is long enough to bring about 

 essentially complete saturation. When all the treatments for a given 

 group of concentrations have been finished (a) the treated blocks are 

 wiped to remove the excess oil, and (b) they are weighed immediately 

 to 0.01 gram. The retentions of creosote or pentachlorophenol, for ex- 

 ample, are determined on a gain in weight basis by calculations from 

 the amount of material picked up during the treatment and the concen- 

 tration of the preservative in the treating solution. 



