14 BULLETIN 101, U. S. DEPARTMENT OF AGRICULTURE. 



it was necessary to adopt some standard by which the classification 

 could be made. The wood was considered easily treated if, under 

 the conditions of these tests, it fulfilled any one of the following con- 

 ditions : 



1. Received an average longitudinal penetration of more than 6 inches. 1 



2. Received an average radial penetration of more than 0.30 inch. 1 



3. Received an average absorption of mora than 15 pounds per cubic foot. 2 



While this basis of classification is to a large extent arbitrary, the 

 specification in regard to radial penetration divides the species which 

 were penetrated by means of the radial ducts from those which 

 were not so penetrated. Woods penetrated radially are, of course, 

 most suitable for treatment in all forms. It was considered, however, 

 that the species which in these tests received an average longitudinal 

 penetration of 6 inches or more are sufficiently penetrable to be 

 treated in short lengths, even though the radial penetration is very 

 slight. The clause in regard to absorption was intended to in- 

 clude, among the easily treated species, those which received a fairly 

 good treatment in the impregnation tests, although neither the longi- 

 tudinal nor radial penetrations determined in the penetrance appa- 

 ratus were especially good. The only woods affected by this clause 

 are the heartwood of redwood and of western larch. 



The species falling in each of the five classes are given in Table 3, 

 together with the penetrations and absorptions of each species. In 

 this table sapwood and heartwood are considered as if separate 

 woods. 



Species in Classes I and II are not very suitable for preservative 

 treatment. While Douglas fir is extensively treated, very severe 

 processes are used. However, the sapwood of both tamarack and 

 Douglas fir can be treated easily. 



Species in Class III are not very suitable for treatment, except 

 in short lengths, on account of the lack of radial penetration. How- 

 ever, western larch and Sitka spruce contain radial ducts and it is 

 possible that by more severe treatments than were employed in the 

 tests these ducts may be penetrated. If western larch be excepted, 

 each species in this class includes both heartwood and sapwood, and 

 such species may be treated therefore without regard to the amount 

 of sapwood present. 



Woods in Class IV permit of thorough treatment. While there 

 is much variation in the penetrability of these species, all are capable 

 of being penetrated readily. 



The woods in Class V can be saturated with creosote in a very 

 short time. All species in Class IV occur in Class V. In actual 

 treating operations the amount and location of the sapwood will 

 determine in which class a given timber shall be placed. 



1 Determined by penetrance tests. 



2 Determined by impregnation tests. 



