Report, Issue 895

Front Cover
U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, 1930 - Forest products
 

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Page 4 - Tracheids and ray cells are not merely bundled together ; they are firmly imbedded in a continuous matrix, the middle lamella, so that there are no spaces between elements through which liquids may move. The air enclosed in wood is mostly enclosed within the tracheids and wood cells. These cavities are not completely isolated from each other as in a honeycomb, however, because their walls are penetrated by small pits, covered by membranes, in which there are ultra-microscopic openings about 0.00002...
Page 6 - The ether soluble extractive of longleaf and slash pines is a resin containing turpentine and rosin. Rosin is a substance of acid reaction capable of forming soaps by • reaction with basic paint pigments. The...
Page 7 - The water-soluble extractives include tannins and other complex organic substances often of an aromatic nature; highly colored carbohydrates; organic acids like formic, acetic, and their homologs; traces of organic nitrogen compounds; and mineral constituents of wood ash. Woods in which the heartwood is strongly colored, such as redwood, redcedar, and walnut, owe their color chiefly to extractives of this class.
Page 4 - ... mm. in diameter, large enough to permit liquids to pass slowly, but far too small to admit paint pigments. In the pines, spruces, larches, and Douglas fir, there are scattered through the structure certain long channels, called resin ducts, running both vertically and radially. These afford long, relatively large passageways provided that they are not obstructed with resin.
Page 4 - They are rourhly from 2 to 4 mm. long by less than 0.03 mm. wide. There are also shorter elements, termed the ray cells, which run along radii of the tree trunk and at ri'-ht angles to the tracheids.
Page 5 - Pieces of wood differ widely in the width of their annual rings, usually expressed as number of rings per radial inch, and in the proportion of springwood and summerwood in each annual ring. If the tree grew rapidly, the annual rings are wide. A high ratio of summerwood to springwood makes wood heavy and strong. Ring width and proportion of summerwood are the most important determining factors in paintability.
Page 4 - Although summerwood has only half the capacity for holding liquids that springwood has, nevertheless liquids move through it much more readily than they do through 'springwood.
Page 4 - Sprin^wood and Summerwood The reason why the annual growth rings are readily distinguishable in wood is clearly revealed in the microstructure because the tracheids of the springv/ood and summerwood differ strikingly from each other.
Page 6 - ... and do not cause any change in dimensions of the wood. Alcohol, however, causes wood to swell slightly. In addition to wood substances, wood contains extraneous constituents which can be removed fairly easily by extraction with suitable solvents and...
Page 4 - Wood structure is cellular, not labyrinthine, so that the porosity is more nearly like that of the honeycomb, in which there is no communication between cells...

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