COAL-TAR AND WATEE-GAS TAR CREOSOTES. 



71 



Table 26. — Comparison of laboratory toxicity tests and service tests on fractions ofcoul-tar 



creosote. 



Material. 



Boiling point at the still. 



Relative 

 position 

 against 

 Fomes 

 annosus. 



Relative 



position 



against 



Xylotrya. 



Relative 

 position 



in 

 service. 



Praction 1 



Below 205" C 



2 



11 



3 



5 



26 



4 



1 1 



2 



3 and 4 



5 



26 



3 and 4 



26 



Traction 2 



205° to 250° C 



5 



Traction 3 



250° to 295° C .,. 



295° to 320° C. . . 



4 



Traction 4 



2 and 3 



Traction 5 



Res. above 320° C 



1 1 







2 and 3 









1 The figure 1 indicates the greatest toxicity or service. 



2 The figure 6 indicates the least toxicity or service. 



Table 26 shows that the toxicity and length of service of the 

 materials tested are almost completely reversed — that is, the highest 

 toxicity gave the least service, and the least toxic substance gave 

 the best service. The discrepancy between these two results is, 

 however, easily explained. In order to exert its effect upon Xylotrya, 

 the toxic principle must be soluble in the body fluids of this organism. 

 In a state of purity these toxic principles would have a great and 

 immediate toxic eJEfect, but this effect would not be permanent, 

 because the toxic principle is taken out by the continual leaching of 

 the water. If, however, these toxic principles are mixed with oils 

 in which they are more soluble than they are in water, it becoines 

 increasingly harder to leach them, because of the retarding action of 

 the oil. If, then, the toxic principles of coal-tar creosotes are con- 

 sidered to be chiefly the lower-boiling oils, it would be expected that 

 in the Petri-dish tests, which are conducted with only a small amount 

 of water, the fractions would arrange themselves in the order 1, 2, 

 3, 4. 5. But in service tests a greater loss would be expected from 

 fraction 1 than from fraction 2, and a greater loss from fraction 3 

 than from fraction 4, and so on. The character of the residual oil 

 in fraction 1 .would tend to approach the character of the oil in 

 fraction 5, and in the end the oils would be much the same in compo- 

 sition; fraction 1 would contain the least, and fraction 5 the most 

 preservative, and the service tests would be expected to show the 

 order 5, 4, 3, 2, 1. This was the actual arrangement in the service 

 tests. 



The separation of the fractions sharply into those indicated in 

 Table 26 is by no means complete. Present knowledge of the action 

 of complex mixtures upon distillation indicates that fraction 1 might 

 be expected to contain considerable material which should have 

 been included in fraction 2, a smaller amount which should have 

 been included in fraction 3, and perhaps a small amount of fractions 

 4 and 5. Fraction 2 might be expected to contain considerable 

 amounts of fractions 1 and 3, and smaller amounts of fractions 4 and 

 5. The truth of these statements is illustrated in Table 27, which 



