f 



EVALUATION OF WOOD PRESERVATIVES 



143 



Retention Gradients 



In the hope of setting at rest some of the doubts and criticisms that 

 have arisen about the accuracy of the treatments and the retention of 

 preservative in the blocks, some results of the treatment process just 

 described will be presented in rather elaborate detail. 



The success of the treatments depends upon experience, as indicated 

 previously, with the particular type of vacuum equipment available. 

 However, once the level of performance to be expected from the vacuum 

 equipment is learned, one has to take into account the variations that 

 are introduced by the density of the blocks and by the specific gravity 

 of the treating solution. It is the intent in all of the treatments at the 

 Laboratories to arrive at a series of gradient retentions, on as accurate 

 a line as possible, and as nearly as possible equal gradients, so that the 

 fairest comparison can be made of the behavior of the different preser- 

 vatives. Fig. 4 shows the gradient obtained by plotting the data shown 

 in Table I for retention of creosote and retention of pentachlorophenol 

 solution over the concentration of these preservatives in the treating 

 solution. The analysis of the creosote — BTL 5340 — is shown in Table 

 II. The slopes of the two gradients are considered to be about as close 

 as the experimental procedure will permit. Fig. 5 shows the gradient 



? 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 



PRESERVATIVE CONCENTRATION IN PER CENT IN TREATING SOLUTION 



Fig. 4— Gradient retentions for comparative soil-block tests of a creosote 

 (BTL No. 5340) and a penta-petroleum solution (4.92 per cent pentachlorophenol 

 in Standard Oil Company of New Jersey No. 2105 Process Oil). The preservatives 

 were used in toluene solution. 



