﻿8 BULLETIN 1128, U. S. DEPARTMENT OF AGRICULTURE. 



that the summer wood and sprint wood merge into each other, not 

 being sharply delimited as in Douglas fir. With experience it 

 is quite feasible to judge with accuracy the relative specific gravity 

 of many of the pieces, leaving the doubtful ones for an actual test 

 or to be worked up along with those below the minimum into parts 

 less highly stressed. In making tests to determine the specific 

 gravity it is not necessary to use the time-consuming immersion 

 method. The pieces can be cut fairly regularly, oven dried, and the 

 volume ascertained by measuring to the nearest half millimeter or 

 to the nearest sixty-fourth of an inch. The weight should be ob- 

 tained as usual. The writer has tested this method extensively and 

 found the limit of error rarely over 0.01. In most cases the result 

 will not vary from that obtained by the immersion method. This 

 method can not be used on irregularly shaped pieces, however. 



In the ring-porous hardwoods, such as ash, it is very easy to 

 determine the relative proportions of spring and summer wood in 

 each annual ring. Here the condition is the reverse of that found 

 in the softwoods. About three-fifths or more summer wood per 

 annual ring in the case of white ash is necessary to give the 

 strength required by the minimum specific gravity of 0.56. Wood 

 with few annual rings to the inch in white ash has a high specific 

 gravity, and this, as a rule, decreases as the number of rings per inch 

 increases. Wood with 20 to 25 annual rings or more to the inch is 

 usually worthless if strength is a requisite. The relations just dis- 

 cussed are fairly constant throughout the ring-porous hardwoods, 

 such as white oak, rock elm, and hickory. 



A large proportion of summer wood is not always an indica- 

 tion of strength in white ash. The notable exception to this rule 

 is pumpkin ash, so called by the trade. This ash has remarkably 

 broad bands of summer wood in the annual rings. These rings are 

 often half an inch broad and contain only one or two narrow lines of 

 pores in the spring wood, but the specific gravity of the wood is low, 

 and when tested in static or impact bending it breaks with a brash, 

 brittle failure under a light load. It can readily be detected by cut- 

 ting with a knife, yielding softly without the resistance offered by 

 good ash. When finished it has a waxy white, cream, or light-brown 

 color in tangential section and can be readily dented with any hard 

 blunt instrument. In cross section the pores in the summer wood 

 sometimes appear as small brown, rather indistinct spots. 



Pieces may be found with almost the same appearance as pumpkin 

 ash which when tested with a knife prove to be hard and tough, 

 with a good specific gravity ; or, again, both hard and soft wood may 

 be found in the same board. 



As nearly as can be ascertained from hearsay evidence, this pump- 

 kin ash is not confined to a particular tree species, but may be found 

 in any of the white-ash group when grown under swampy conditions 

 in the southern part of the range. It does not necessarily occur, 

 but when it does the central portion of the butt logs or even the entire 

 trunk may be composed of such wood. Pumpkin ash has been as- 

 signed by botanists as the common name for one definite tree species 

 {Fraxinus profunda Bush), but the name as applied in the lumber 

 trade denotes white-ash wood having the characteristics above de- 

 scribed without regard to species. 



