HARDWOOD RECORD 



27 



One-half of these boards can be treated in the baby cylinder, and the 

 other half left to dry as in ordinary practice, either in the air or in 

 a kiln. This will enable the experimenter to make a comparison of 

 the shrinkage, time for drying, staining, checking, weight, etc. It 

 will be well to mark the weight and accurate measurement on every 

 piece of lumber and place both the steamed and untreated lumber 

 on sticks for drying in the open or in a kiln. In this manner the 

 steamed pieces wUl be subjected to harsher conditions than if the 

 entire pUe were of treated lumber. 



It is recommended in making this experiment that a steam pressure 

 of twenty pounds be used as a basis, subjecting the wood in pre- 

 liminary experiments to ten minutes at this pressure for each one-inch 

 in thickness, i. e., ten minutes for inch lumber, fifteen minutes for 

 one-and-a-half-inch, and twenty minutes for two-inch lumber. This 

 scale of pressure should be a base, but the time is only approxi- 

 mate. What one must seek to do is to give the wood time enough 

 under this pressure to insure the steam getting to the center of the 

 board, but never by any possible chance to give the lumber so much 

 time in the steam as to injure the fiber of the wood. In no case 

 should a steam pressure of over forty pounds be attempted, as beyond 

 this there is certainty of danger in injuring the strength of the fiber. 



Whatever can be attained in the results involved in a section of 

 twelve-inch pipe can be duplicated in a ten-foot cylinder. This is an 

 experiment that costs but a very small amount of money, and it is 

 thoroughly believed is worth trjring out by everyone who is having 

 the least difficulty with seasoning defects, stain, shrinkage or excess 

 weights on lumber products. 



The Forest Service, through its Madison, Wis., Forest Products 

 Laboratory, has been making exhaustive experiments in the prin- 

 ciples underlying drying lumber, and while those in charge have 

 devoted more time to kiln-drying than they have to steaming wood 

 under pressure, Harry D. Tiemann, in charge of the timber physics, 

 alleges: 



' ' The advantage of having the timber heated thoroughly before 

 it goes into the kiln is that heat renders the wood more susceptible 

 to the transmission of moisture. Since the water is evaporated from 

 the surface only and must pass from the interior of the wood to the 

 surface in order to be evaporated, the desirability of having the wood 

 thoroughly warmed when the dry-kiln treatment begins is obvious. 

 Where the wood can stand the heat without detrimental effects for 

 the intended use, prelim in ary steaming, not in condensed but in live 

 steam, is beneficial. This not only accomplishes the desired heating, 

 but it assists in the transmission of moisture from the center also 

 by moistening the surface if it is too dry. On the other hand, steam- 

 ing temporarily softens the tissue of the wood so that it becomes 

 more or less plastic, as is well known in the wood-bending industry. 

 Other effects, also, are produced which to a greater or less extent 

 change the properties of the wood. The organic materials or 'sap' in 

 the wood are changed by 'cooking,' and apparently some undeter- 

 mined chemical change takes place in the ligno-cellulose of the wood 

 itself. This is indicated by the fact that the color of the wood is 

 darkened, the degree of coloring depending upon the temperature and 

 duration of the process, and that the wood, when subsequently dried, 

 has lost some of its original weight and is less hygroscopic. The 

 change in hygroscopicity is beneficial for some purposes, as it reduces 

 swelling and shrinkage of the wood, but the wood is less resilient and 

 if soaked it becomes softer than the unsteamed material and in 

 extreme cases even 'punky. ' 



"The pressure and duration of steaming desirable in kiln-drying 

 are points which have not yet been thoroughly worked out. From 

 five minutes to twenty-four hours, or even longer, and pressures 

 ranging from atmospheric to fifty pounds gauge have been used in 

 practice. The higher the pressure the greater is the effect produced, 

 and the longer the time the more thoroughly the treatment penetrates 

 the wood. Experiments have shown that a pressure slightly above 

 atmospheric for twenty-four hours is sufficient to slightly darken two- 

 inch maple clear through, and a pressure of forty pounds will turn 

 oak and probably other hardwoods almost black. Even where the 

 strength of the wood is not the primary consideration it probably is 

 not safe to exceed fifteen pounds gauge pressure (250 degrees F.), 

 except for special purposes. ' ' 



The writer does not fully agree with Mr. Tiemann in all the state- 

 ments he makes, because repeated experiments have demonstrated that 

 steam-treated lumber under a maximum of twenty pounds pressure 

 and for a limited period loses none of its resilience, and in no case 

 ever becomes "punky." There is no good reason in commercial 

 practice to steam wood any longer than is necessary to force the 

 steam to the center of the plank. Any steaming beyond that pos- 

 sesses no value and is very likely to affect the strength of the wood. 

 There would be no good reason to leave wood in a steam tank under 

 pressure for twenty-four hours, but certainly if this were done it 

 would be expected that the wood would be materially darkened and the 

 general tone deadened. Furthermore the l)reaking ami crushing 

 strength of the wood would be lessened, and its value deteriorated. 



It is a fact that can be substantiated that steamiag lumber under 

 pressure for the proper length of time livens the tone, brightens the 

 color, increases the resilience, greatly improves its working qualities 

 and reduces the tendency to swell to almost nil, and even prevents 

 "raising the grain" when the water stains or fillers are used, 



H, H, G. 



Supply of Paper Birch Not Decreasing 



The U. S. Department of Agriculture is authority for the state- 

 ment that the paper birch, often called also white birch, or canoe 

 birch, is one of the few timber trees in this country which seem 

 to be holding their own against ax and fire. The average citizen 

 probably takes no particular interest in the paper birch. Yet it is 

 doubtful if any other kind of wood on the face of the earth is 

 found in so many households; for paper birch furnishes most of 

 the spools made in the United States. 



Maine is the chief center of spool manufacture. Its factories turn 

 out 800,000,000 spools yearly, chiefly birch. Few woods as hard as 

 this can be worked with as little dulling of the tools; its principal 

 recommendation lies in that fact. It is handsome in color, and, after 

 the wood becomes seasoned, it shrinks and warps very little. That 

 is an important consideration, because the delicate machinery that 

 winds the thread would fail to work if the spool changed its shape 

 to a perceptible degree. 



The birch wood for spools must be selected and handled with care. 

 The tree 's red disk heartwood is objectionable because it will not 

 turn smooth in the lathe, and the color is not desired. Few indus- 

 tries waste more wood, in proportion to the quantity used, than 

 spool making. Heartwood, knots, and all other defects, frequently 

 amounting to more than one-half of the tree, are rejected. From 

 one-half to three-fourths of the remainder may go to the refuse 

 heap in sawing the bars and turning the spools. Despite this waste 

 the paper birch does not appear to be threatened with extinction. 

 It is a fire tree — that is, it spreads rapidly over spaces left vacant 

 by forest fires. The most extensive paper birch forests of Maine 

 and New Hampshire occupy tracts which were laid bare by the 

 great forest fires which swept the region from 1825 to 1837. 



The tree is short lived. At an age when the white cedar, for 

 example, is just beginning to lay on useful wood, the paper birch 

 has passed its prime and is ready for decay. It is placed at still 

 further disadvantage by being unable to compete with other trees 

 for light and soil. It prospers when growing alone, but it gives up 

 the fight after stronger trees begin to crowd it. Nevertheless, it 

 is believed that more paper birch is growing in the United States 

 todav than two hundred years ago. 



The Forests of Mindoro 



A description of trees, forests, and forest conditions in Mindoro, 

 one of the Philippine islands, has been prepared by Melvin L. 

 Merritt and published at Manila by the Bureau of Forestry. It 

 is written in a popular style and is largely free from the long 

 lists of unpronounceable names which so often make up the chief 

 parts of Philippine reports. It is easy reading, and an enter- 

 taining picture is presented of conditions in that remote part of 

 the world. 



