169 



The rate of loss from treated wood in air is not nearly as great, especially at first, 

 as would be expected on the basis of the loss from the open dish. In fact, the form 

 of the two loss curves is different throughout their whole range and the rate of loss 

 from treated wood reaches a fairly constant value at a much smaller percentage loss 

 than in the case of the ojien dish. This indicates that the surface of the treated wood 

 does not act as a free oil surface. However, the rate of loss from the treated surface 

 is dependent on the rate of feeding of low boiling constituents to the surface, which 

 would probably be consideral)K' lower than in the free oil, merely on account of the 

 cutting down of circulation in the oil. This is substantiated by the slightly increased 

 amounts of low boiling constituents found as we go inward through the treated wood. 

 If the rate of feeding to the surface were rapid, the composition of the oil should 

 remain constant throughout the treated wood. The same slight composition differ- 

 ences in different layers are also shown by a thirty-year-old pile from the Oakland 

 Long Wharf. There is also a possibility that the rate of feeding to the surface is further 

 limited by an actual absorption of the oil by the wood, cutting down the effective 

 vapor pressure of the oil. In either case (and particularly in the latter), the nature 

 of the wood used would be likely to have a considerable effect upon the rate of loss. 



TABLE 18 

 •LOSS OF CREOSOTE BY LEACHING AND EVAPOR.ATION 



*A11 losses corrected to same mass of oil and same exposed surface. 

 tSome mechanical loss (possibly as much as 1 per cent) in sampling. 



On this basis it appears that no evaporation study of free oil is of \alue, except, 

 in a very general way, in determining the probable rate of loss from treated timbers. 



The smaller rate of loss from treated wood in water as compared with treated 

 wood in air indicates the advisal^ility of storing creosoted timbers in water when 

 possible'. Probably the reason for the smaller loss in water can be ascribed roughly 

 to the greater volatility than solubility of creosote constituents in general. Also the 

 rate of feeding to the surface is probably cut down by the swelling of the wood in 

 water, which is not prevented by the presence of oil, because water can penetrate 

 the cell walls of wood while creosote does not do so. 



In addition to knowing the absolute loss of creosote from treated wood, it is 

 important that we know on what constituents this loss falls. To do this, we must be 

 able to effect complete recovery of the oil remaining in the wood, without altering 

 its character. Experiments on the use of benzene as an extracting solvent indicate 

 that with it the oil can be completely recovered in an unchanged condition. The 

 Committee work had the benefit of detailed knowledge of the oils originally used in 

 all such tests, including carefully preserved identical samples; the lack of which has 

 invalidated, or at least cast doubt upon, most previous attempts in this direction. 



'The advantage of water storage may be offset by the increased rate of loss of tar acids, especially 

 if storage is for a long time. 



