to prevent excessive checking but sufficiently rapid to be commercially practical. This optimum moisture gradient curve furnishes the basis for the calculation of a proper drying schedule. AIR-SEASONING METHODS OF PILING A in Figure 23 illustrates one of the approved methods of piling small dimension stock. It will be noted that the stock itself is not used for stickers, but that stickers are used which are somewhat FIGURE 25.-Shed piling is one of the best methods of air smaller than the stock. It will also be noted that the piles are well covered, carefully spaced, and without slope. Figure 24 illustrates a method of piling the larger sizes of readycut stock which is commonly used but which is objectionable in some respects. It will be noted that green stock is used for stickers, and that the air spaces are unnecessarily large. No covering is provided for the piles. In some cases a full course of stock is used instead of the three crosswise stickers as illustrated. However, this method should not be used unless it is desired to reduce the rate of seasoning to a minimum. In either case the use of green stock for stickers encourages infection by stain fungi. In air-seasoning some species of small dimension stock it will be found that most of the surface checking occurs on the plain sawed surfaces. This is primarily due to the fact that shrinkage on these surfaces is generally much greater than on the quarter sawed or radial surfaces. In some species in which the medullary rays are unusually large, such as the oaks, it is believed that the presence of these rays on the quartered surfaces decreases the rate of drying from these surfaces, thus also increasing the tendency to check on the opposite, faster drying, plain sawed surfaces. The United States Forest Products Laboratory recommends that oak small dimension FIGURE 26.-A method of piling small dimension stock which stock be piled so that the quarter sawed surfaces are turned toward the top and bottom of the pile, next to the stickers. The plain sawed surfaces are brought close together in each layer of the pile. This method of piling slows up the rate of drying on the plain sawed surfaces and exposes the quartered surfaces to more severe drying conditions. Obviously this method can not be successfully applied to all species of ready-cut stock. It is usually advisable to build piles which are narrow and not too high. The advantage of building narrow piles is that they may be built up quickly and covered, or built up to the shed roof. Expo sure to the sun and wind for a very short period may cause checking. Wide piles also decrease the rate of circulation and therefore slow up the rate of drying. The disadvantages of building high piles are that they require a longer time to complete and are more liable to topple over. PILE FOUNDATIONS Although it is not good practice, a large number of pile foundations are constructed entirely of untreated nondurable wood because of a saving in the original cost. Pier foundations of concrete, treated wood of nondurable species and untreated wood of durable species offer the advantages of permanency, immunity to decay, and the supplementary advantage of eliminating the spread of decay through the piles. These piers should be large enough to offer a firm foundation, should have the bearing surfaces at least 12 inches above the surface of the ground, and should be set well below the frost line. PILE COVERS Several specialized types of pile covers, such as corrugated galvanized iron, have been developed, but the common practice is to roof piles with low-grade stock. In most cases No. 3 common and lower is used, and often these old pile covers are placed on new piles until they are no longer usable. It is essential that small dimension stock be quickly and properly piled after manufacture, and that the stock on the tops of the piles be protected from rain and from the too rapid seasoning caused by sun and wind. This protection may be given by a pile cover or by a shed. Shed piling has the advantage of giving the stock more complete protection and is very desirable in most cases. If the sides and ends of the shed are inclosed, additional protection is given to the material. Sheds are especially desirable when the stacks are built up rather slowly or when the stock must remain in green storage for a considerable length of time, since the stock is protected from the direct rays of the sun. Attention is called to the fact that the more complete the inclosure the slower will be the drying rate. This may be an advantage or a disadvantage, depending on the species and moisture content of the stock being dried and on the atmospheric conditions. Care must be used in shed drying those species which stain easily, since poor ventilation may result in staining to such an extent that some of the stock must be rejected. If shed space is not available for air seasoning, the piles should be provided with a rain-tight cover such as is shown in Figure 23 A, which extends over the sides and ends. A cover should have enough slope to carry off the rain. STICKERS It is not common practice to use stickers in connection with the piling of ready-cut stock for air seasoning. When narrow piles are used it may be inadvisable to use stickers because of the cost of manufacturing and handling short crossers. When the stock is stacked in wide piles, stickers could be used to advantage. Wellseasoned stickers prevent the occurrence and spread of stains and molds, and thin stickers will decrease the rate of drying, when this is desired. In both air seasoning and kiln drying the use of stickers permits the piling of a larger quantity of the stock in a given space than when the stock is used as stickers. Stickers should be of uniform thickness, well seasoned, and have a length a few inches in excess of the width of the pile. PREVENTION OF END CHECKING In seasoning thick or wide stock end checking usually causes considerable degrade, especially in the hardwoods. End coatings are sometimes used to decrease the degrade caused by end checking. A brush treatment of paint or some special preparation may be used. Paints with a coal-tar base have been tried for this purpose, but they do not adhere well to green stock. A filler which is more satisfactory than either paint or whitewash has been recommended and is prepared according to the following formula: One pint of glue in solution and 3 quarts of salt to three-fourths of a barrel of whitewash. This filler will last for about two years. The following coatings are recommended by the Forest Products Laboratory: A cold coating called "gloss oil" is made up of 8 parts of quicklime, 100 parts rosin, and 57.5 parts spirit. To 100 parts of the gloss oil add 25 parts barytes and 25 parts fibrous talc. It is not intended that the gloss oil be made up by the user; it should be purchased from the varnish manufacturer. The formula is included so that there will be no mistake as to the kind of gloss oil required. The hot coatings recommended are coal-tar pitch, and a mixture of rosin and lampblack (100 parts of rosin to 7 parts of lampblack). Paraffin, asphaltum, and white or red lead oil have also been recommended for this purpose. Of the compounds mentioned the paints, leads, oils, whitewash compound, and gloss oil can be classified as cold coatings, while coal-tar pitch, rosin and lampblack, paraffin, and asphaltum are classified as hot coatings. The coatings mentioned in the first group are liquid at ordinary temperatures and can be applied cold. The coatings included in the second group are solid at ordinary temperatures and must be applied hot. Either the cold or hot coatings can be used effectively in temperatures up to 140° F. The hot coatings are usually more effective than the cold coatings for temperatures between 140° and 170°. No coating has been found which is entirely satisfactory for temperatures higher than 170° F. Paraffin is effective during air seasoning but can not be used in kiln-drying because of its low melting point. To prevent checking in thick stock, the front and rear of the piles are sometimes covered with cull lumber for the purpose of warding off the direct rays of the sun. Placing the piles close together will also reduce the amount of checking. SAP STAIN 1 Sapwood of many species is susceptible to staining during the early stages of the seasoning process. These stains are of various colors, such as blue, blue-black, gray-brown, green, red, or yellow. The various colors are due to the color of the fungus which feeds on 1 See Sap Stains of Wood and Their Prevention, National Committee on Utilization, 1929. Wood the cell content of the wood. These fungi do not affect the strength properties of the wood during the early stages of development. The southern yellow pines are susceptible to blue stain, especially during moist, warm weather. The most practical known method of preventing blue stain is to kiln-dry the stock green from the saw. If this method is impractical, treatment with an antiseptic dip is recommended. Sodium carbonate (soda ash), and sodium bicarbonate (ordinary baking soda), are the two dips most frequently used. Neither is a perfect preventive, but either will go far toward avoiding stain. Yellow stain is often found in hardwoods. The presence of this stain is first shown by a moldy appearance of the stock. Like all sap stains, yellow stain mars only the appearance of the material but is highly objectionable in most cases. This stain may be avoided by rapid seasoning, steaming, storing in a dry place, or treatment with preservatives. DECAY AND YARD SANITATION A large amount of the material which decays while in service has been infected while in storage. Much of this infection could be prevented by inaugurating sanitary conditions in the yards in which this material is stored. Decay in wood is due entirely to fungi. To understand the action of fungi, it is also necessary to understand that these organims are in reality a low form of plant. The destructive action of fungi is caused by small, threadlike, branched filaments called the "mycelium." The mycelium secretes chemicals called "enzymes," which dissolve the various wood elements into food for the growth of the fungi. This reaction results in the decay of the wood which is attacked. Fungus infection may be spread in two ways-by means of minute spores, corresponding to seed in the higher forms of plant life, from the fruiting bodies of the fungous growths, and by means of the mycelium. The spores may be spread by the wind and various other agencies. Contact of sound wood with infected wood will permit the infection of the sound piece by means of the mycelium. Since fungi are a form of plant, they require certain conditions for their growth and reproduction. These conditions may be classified as follows: Food, moisture, suitable temperature, and air. If any one of these four factors is eliminated, attack by fungi is impossible. The common methods of preventing decay are preservative treatments, which poison the wood so that it is not usable as food, and rapid seasoning, which reduces the moisture factor to the point where fungous growth is impossible. Below are given some of the approved methods of preventing and reducing decay infection during yard storage and seasoning: Drainage. Small dimension stock should be piled on well-drained soil and on a location which will not be exposed to floods, high tides, and standing water. Débris and weeds.-All rotting débris should be removed and burned. Decayed foundations and tramways should be replaced. Weeds should be cut away from pile foundations to improve ven |