Page:The New International Encyclopædia 1st ed. v. 17.djvu/670

* SAW. 602 SAWMILL. cut at riplit nnglcs to the filnc of tlip wood, while in the latter tlioy are adapted to cutting in the direction of the lihre and are alternately Ijent or set so that they make a hroadcr cut than the thickness of the blade. The handsaw has a blade broadi'r at one end than the other, and a wooden handle tixed to the lirnader end. During the ninctwntli century the ciiciilar nuw, jiatented by Samuel .Miller in Knglaml in 1777, canie into universal use wherever machinery could l)e had for working it. It i.s generally so iitted as to be worked under a Hat bench, a part only of the blatle projecting through a narrow slit cut in the top of tiie bench. It is revolved with great rapidity, and the wood resting on the bench i.s pushed'against the saw. Circular saws are made in diameters from 1 inch to 70 inclies, and are extensively used in sawing logs into boards, jdanks. and other forms of timber. (See Saw- mill; Woon-WoKKlN'O Machixekv.) The band- saic was invented in 1S08 by William Newberry, an Englishman. It consists of a very long band or web, as it is called, of steel, usually very narrow, and with finely cut teeth. The two ends are joined together so as to form an endless band, •which is passed over two revolving drums, one . above and the other below the working-bench, through holes in which the saw passes. The cylinder sniv or crown saw is another variety, which was an invention of great antiquit}'. It is used for cutting curved staves for barrels, button blanks, sheaves, and other special forms. (See Cooi'ERAGK. ) For descriptions of saws for metal-working, see Metal-Working Machinery. SAW All, sa-vl'e. The largest of the Samoan Islands. See Savaii. SAWDUST. A by-product obtained from sawmills and other wood-working machinery. Besides its uses as a packing material, a stuffing for dolls and cushions, and an absorbent covering for floors, such substances as vegetable charcoal, tar, oxalic acid, and wood alcohol are made from it. In preparing oxalic acid the sawdust is fir.st saturated with a concentrated solution of soda and potash in the proportion of two of the former to one of the latter: it is then placed in shallow iron pans, imdcr which flues run from a furnace, whereby the iron pans are made hot, and the saturated sawdust runs into a semi-Huid pasty state. It is stirred about actively with rakes, so as to bring it all in contact with the heated surface of the iron, and to granulate it for the succeeding oiierations. It is next placed in similar pans, only slightly heated, bj' which it is dried. In this state it is oxalate of soda mixed with potash. It is then placed on the bed of a filter, and a solution of soda is allowed to per- colate through it. which carries with it all the potash, leaving it tolerably pure oxalate of soda. It is then transferred to a tank, in which it is mingled with a thin milk of lime, by which it is decomposed, the lime combining with the acid to form oxalate of lime, and the soda being set free. Lastly, the oxalate of lime is put into a leaden cistern, and sulphuric acid is poured in; this takes up the lime, and sets free the oxalic acid, which readily crystallizes on the sides of the leaden eisteiii. or on pieces of wood placed there for that purpose. In making charcoal the sawdust from hard and soft woods must be kept separate, as the former requires much more intense heat than the latter. After careful sifting the sawdust is carbonized in fireclay, plumbago, or cast-iron retorts. The resulting charcoal i.s sifted to re- move the calcareous matter which has been de- tached during the burning process. This char- coal is used to remove unpleasant flavors from wine and as a filtering medium, especially in distilleries. An English patent was taken out in 1890 for making an artificial wood from a mixture of sawdust and certain quantities of gums, resins, or other suitable agglutinants, either in a dry state or dissolved, the com])ound being subjected to pressure at a temperature high enough to melt the gums. According to another English patent, taken out a year later, sawdust may be so prepared as to be non-inflannnable, to be used as a jacketing for boilers and similar purposes. Sawdust, like other wood, may also be distilled by a proc- ess which not only saves the charcoal, but also furnishes such products as alcohol and tar. SAWFISH. One of the elongated, shark- like rays of the family PristidiP, remarkable for prolongation of the snout into a tlat bony sword, armed on each edge with about twen- t}' large bony teeth, a formidable weapon for killing prey among shoals of fishes, slaj'- ing them right and left. Whales are said to be killed by saw- fishes occasionally, and the saw has been some- tooth of a sawfish. times driven through Section of the rostrum in- the hull of a ship. <^!"'^i°B "J"', *°"* '■■ • ''• "«: ., . „ . ^ sified part of rostrum; c, t'aTial About five species are tor vessels euppl.viuK the known, living in the tooth; d. medullar.v cavity of warm seas. One, the '^ni2l%%fn: "' '^■""""^ 'pez sierra of the West Indies, is common about Florida and in the Gulf of Mexico, and ascends the Mississippi and other Southern rivers. It is often 15 feet long, a fourth of which measures the 'saw.' It plays havoc with fishermen's nets. See Plate of Lam- prey.? and Dogflsh. A family of sharks (Pristiophoridae) similarly armed occurs in the Pacific Ocean. SAW-FLY. A hjmienopterous insect of the superfaniily Tenthredinoidea, so named on ac- count of the saw-like ovipositor of the female, which serves to drill holes in vegetable tissues and to assist in conveying the eggs into these holes. The saws are mechanically perfect tools. About 2000 species are known, most of which are found in temperate and cold regions. Many saw-flies in the larval stage are highly injurious to vegetation. The largest of the com- mon North American saw-flies is Cimbcx Ameri- cana, whose eggs are laid in the leaves of the elm, birch, linden, and willow. See Rose In- SECT.s : Pear In,sects ; Currant Insect.s. SAWMILL. The mill or machine by which logs are sawed into boards and timber; by popu- lar extension, the building, with its machinery, ia which timber is sawed. The first form of saw-