SLB 6 



which covers the fused metals in the 

 smelting-hearths. The slag of iron-works 

 is usually called cinder, and is commonly 

 bi-silicate of lime and magnesia, with a 

 mixture of some metallic oxides. 



SLAM. The name given in some' parts 

 to the refuse of alum- works. 



SLAT. A stretcher. See SLOAT. 



SLATE, Fr. tclater; Ir. sglata. In 

 mineraloiiy, a genus of which the species 

 are 1. Mica-slate, a mountain rock, of 

 vast extent, and of schistose texture. It 

 is sometimes employed for covering 

 houses. 2. Clay-slate, a simple schis- 

 tose mass, of a bluish-grey or greyish- 

 black colour, of various shades, exten- 

 sively distributed in Britain, and much 

 used for covering houses ; and hence 

 called roofing-slate. The finer straight 

 foliated varieties are employed as writing- 

 slates ; and the softer and more compact 

 varieties are made into slate-pencils. It 

 is closely connected with the mica-slate. 



3. Whet or hone slate is a slaty rock, 



containing a large proportion of quartz, 

 used as a whet-stone or hone. It occurs 

 in Saxony, Bohemia, and the Levant, 

 (whence it takes the name of Turkey- 

 hone), and also in the valley of Llanberris 

 in North AVales. 1. Polishing-slate is a 

 siliceous slaty mineral, found in Bohemia. 

 It is supposed by some to be formed of 



microscopic shells. 5. Drawing-slate, 



or black-chalk, is of a bluish-black colour, 

 occurs in mass, and the longitudinal 

 fracture is slaty and glimmering. It con- 

 tains about 11 per cent, of carbon, and is 

 used in crayon-drawing, and for writing 

 on paper and other materials. The best 

 conies from Italy, Spain, and Trance; 

 but it also occurs in the Island of Islay 



of fair quality. 6. Adhesive-slate is of 



a greenish-grey colour, and adheres to 



the tongue. 7. Bituminous- slate is a 



soft species of sectile-slate clay, impreg- 

 nated with bitumen. 8. Slate-clay, or 



shale, is a stratified member of the coal- 

 measures. It is simply indurated clay. 

 There are several varieties of these 

 species, as chlorite - slate, alum -slate, 

 grauwacke-slate, &c. 



SL.VT'ER. 1. One whose business is to 

 cover the roofs of buildings w ith slates. 



2. In entomology, see MILLEPED and 



Oxiscrs. 



SLATE-SYS'TEM. In geology, compre- 

 hends the Plynlymmon rocks, the liala- 

 limestone, and the Snowdon rocks. In 

 the strata of this system are found the 

 most ancient organic remains. 



SLED, ) A description of vehicle which 



SLEDGE. j moves on runners, much used 

 for conveying heavy weights, as timber, 

 stones, &c. over soft ground, or- where 

 there are no proper roads. In England 

 the name sledge is commonly used; in 

 the United States of America sltd is the 



6 S L 1 



term. The sleigh is somewhat different. 

 resembling the vehicle called in Scotland 

 a car. The sled has p:perly no trams, 

 but is dragged like a 'narrow by means 

 of chains or the like ; the sleigh or Scot- 

 tish car differs from a cart or waggon 

 only in being sligluer made and having 

 no wheels. 



SLEEP'ERS. 1. Among builders, timbers 

 laid upon dwarf walls for supporting the 



ground-jjpists of floors. 2. Generally, 



cross horizontal timbers for fixing plank - 

 ing or the like where it is necessary 

 to fill under, in order to make a secure 

 foundation. The sleepers upon some 

 railways are of stone ; but wood is pre- 

 ferable as being more elastic. 



SLEET. 1. In meteorology, a fall of rain 

 and hail or snow together. 2. In gun- 

 nery, the part of a mortar passing from 

 the chamber to the trunnions for strength- 

 ening that part. 



SLEETCH. The thick mud lying at the 

 bottom of rivers. 



SUCH, j The ore of any metal, but par- 



SLICK. j ticularly gold, when it has 

 been pounded and prepared for further 

 working. 



SLICK'ENSIDES. In mineralogy, a pro- 

 vincial name of a variety of galena, 

 found in Derbyshire. It takes this name 

 from its peculiarly polished surface. 



SLIDE. In mutic, a grace used in 

 Germany, consisting of two small notes 

 moving by degrees. 



SLID'ING-RULE. A mathematical in- 

 strument, having one or more slides or 

 parts, which slide into grooves in the 

 stock of the instrument. It is much used 



in gauging, and other kinds of mensura- 

 tion, and is often very convenient, as thw 

 computations are performed by it with- 

 out the aid of compasses, merely by the 

 sliding of the parts of the instrument, 

 one by another, the lines and divisions of 

 which give the answer or amount by in- 

 spection. The instrument is variously 

 contrived and adapted to particular pur- 

 poses: for instance, Everard's sliding- 

 rule is used in cask-gauging; and Cog- 

 geshall's in measuring the superficies 

 and solidity of timber, masonry, brick- 

 work, &c. 



SLID'ING-KEEL, used in small boats. A 

 false keel let down through the bottom 

 to hold against the wind. 



SLIP. 1. Slipping of the earth of an 

 embankment, cut, &c., aiising from want 

 of stability of the soil, badness of foun- 

 dation, &c. 2. A place having a gra- 

 dual descent on the bank of a river, har- 

 bour, &c., convenient for ship-building. 

 3. Matter, such as that found in ti4 



