GROUND-WOOD PULP. 49 
MICROSCOPIC COMPARISON OF GROUND-WOOD FIBERS. 
Plates IV to XII are photomicrographs of the ground-wood fibers 
: obtained from the various species tested. It is not possible, of 
course, to gauge accurately from such photographs the pulp-making 
qualities of the fibers. Length of fiber does not necessarily mean 
strength, for a stronger pulp can be obtamed from fibers which, 
though quite short, will felt well. Steamed white birch pulp, for 
example, will test as high in strength as longer-fibered material from 
i the pines, larches, and hemlocks. However, the photographs make 
" it possible to compare the characteristics of the fibers of one kind of 
_ wood with those of another kind, especially since the lodgepole pine, 
: aS 
Cane ; 
pine, hemlock, and tamarack were ground under the same conditions 
: of pressure, speed, surface of stone, etc. For some of these species 
_ photographs of both cooked and uncooked fibers are shown. The 
_ cooked-wood specimens were not treated in the same manner, nor 
were they ground under like conditions. 
In the case of birch (PI. IV) it will be seen that the uncontecd pulp 
1s very short and contains much wood flour, while the cooked fibers 
are fairly long and very fine. When run into paper without the 
addition of sulphite the steamed pulp showed a strength under test 
‘of 0.51 poimt per pound and 5.8 pone per thousandth inch of 
thickness. 
14852°—Bull. 848—-16—_4 
