24 BULLETIN 1485, U. S. DEPARTMENT OF AGRICULTURE 
both are of immense importance from a practical standpoint, since 
it is customary to keep on hand at the mills at least one year's 
supply of pulp wood, and since much of the wood is in storage for 
considerably longer periods. Balsam fir, for example, shows admir- 
able pulping qualities by any of the processes and yet is not well 
regarded by the industry, for the reason that it is very susceptible 
to both insect attack and decay. Although red alder is a wood 
excellently adapted to the manufacture of soda pulp, unless methods 
of handling can be devised whereby loss from its excessive suscepti- 
bility to decay may be avoided its use as a pulp wood will remain 
out of the question. Reference works on the pathological and 
entomological characteristics of various species are available and 
should be consulted in any particular case. 
The fiber lengths stated are the averages of such measurements, 
often very limited in number, as have been made by the Forest 
Service or, where Forest Service measurements are not available, 
by other investigators. They offer only an indication of what may 
be expected from the species given. Since many of these measure- 
ments were made the significance of a further element, namely, the 
position of the fibers in the tree with reference to height, has been 
investigated in considerable detail. It has been found that the fiber 
length in one tree may vary from 0.8 to 7.65 milimeters 4 or even 
from 0.3 to 8.6 milimeters. 5 The length of the fibers undoubtedly 
affects the character of the pulp obtainable. The fineness of the 
fiber is also a very important characteristic. 
Physical properties, however, considered alone, may lead to 
contradictory conclusions. Thus rather poor and tender pulps 
were obtained from redwood with a fiber length of 53^ milimeters, 
whereas an extremely tough and durable sheet was obtained from 
yellow birch sulphate pulp with a fiber length of only 1 Yi milimeters. 
The substance forming the fiber is of great importance in this respect 
and varies with different species as well as with different treatments. 
The information on color and quality given in the summaries 
under the heading " Unbleached pulp" has particular reference to 
uses in which bleaching is not ordinarily practiced. Sulphite pulp, 
for instance, is often used without bleaching, as in conjunction with 
mechanical pulp in the manufacture of newsprint, and for that 
reason it must be light in color and free from shives. Sulphate pulp 
for wrapping paper is seldom bleached. 
In other large uses, however, bleaching qualities are important. 
Exceptionally well-operated mills bleach spruce sulphite with as 
little as 10 per cent of bleaching powder of standard strength, but 
the average is well over 15 per cent. Some mills are using as much as 
25 per cent on pulp obtained from the species available and yet are 
showing a profit. 
Under the characteristics of sulphate pulps from the pines the 
bleach consumption in two stages is often shown. Tests indicated 
that in this case the consumption was only half that required in one 
stage and the color obtained was a purer white. Not all species 
were so tested, however, and the fact that the bleach requirement 
for two steps is not mentioned does not mean that better results 
4 Gerry, E. microscopy of pulpwoods. Paper, Apr. 21, 1920. 
* Lee, H. N., and Smith, E. M. douolas fir fiber, etc. For. Quart., Dec, 1916, 
