SMOKE 841 



2-6. It adheres to the tongue, and crumbles down when immersed for some time in 

 water. It is the Killas of the Cornish miners. 



In addition to the slates properly so called, many fissile rocks, which split along 

 planes of bedding into sufficiently thin slabs to be used for roofing, are popularly 

 called ' slates.' Thus the 8tonesfield slate is a thin-bedded arenaceous limestone, at the 

 base of the Great Oolite, largely quarried at Stonesfield, in Oxfordshire. The Colley- 

 weston slate is a similar fissile limestone, belonging to the Lincolnshire (Inferior) 

 Oolite, which is "worked at Colleyweston, in Northamptonshire, and is much used by 

 Sir Gilbert Scott for roofing churches built in the Gothic style. The Duston slate is 

 a similar material occurring in the Northampton sands. 



SLATY CLEAVAGE. See CLEAVAGE. 



SLIDES. A miner's term for a dislocation of the strata, which is evidenced by the 

 sliding of one portion of the rock over the other. These slides are often, but not always, 

 filled with a softer matter than the rock, a clay in a greater or less state of induration. 



SXiIKENSIDES. The name given to smooth striated surfaces of rocks or of 

 mineral lodes, indicating the grinding action of the movement of heavy masses. Many 

 polished surfaces are called slilcensides to which the term is evidently inapplicable. 



SKIP. A fracture of strata, "with the levels of the relative beds altered on the 

 opposite sides of the fracture : the beds are thus slipped out of their original position. 



SLOKE. The common name for laver. See ALGJE. 



SIVXAIiT. A beautiful blue glass made by melting cobalt ore with flint and potash. 

 It is largely prepared in Saxony ; for an account of its manufacture, see COBALT. The 

 chemical composition of a specimen of German smalt was as follows : Silica, 66'20 ; 

 potash and soda, 16'31 ; oxide of cobalt, 6'49 ; alumina, - 43 ; oxide of iron, 0'24 ; 

 arsenic, a trace ; "water, &c., 0'57. 



SMALTINE. See COBALT. 



SMECTITE. A name given to a kind of fuller's earth, found in Lower Styria. 



SMITHSONITE. See CALAMIKB ; ZINC. 



SMELTING. The processes for obtaining the metals from the ores. These are 

 described under their respective heads. See COPPER, IRON, LEAD, SILVER, TIN, ZINC, &c. 



SMOKE. The more volatile portions of coal, passing off, charged with finely- 

 divided carbon, at a comparatively low temperature. 



If the black smoke, "which escapes from a furnace when a quantity of cold coals is 

 thrown in upon an incandescent mass, can be made to pass over another portion of 

 coal in active combustion, this carbon is consumed, i.e. combined with atmospheric 

 oxygen, and converted into carbonic oxide, which burns, producing carbonic acid ; 

 and it therefore eventually escapes as colourless vapour. 



One great cause, and perhaps the greatest cause of the annoyance of smoke in large 

 towns is the carelessness of the man supplying fuel to the fire. Where coal is abun- 

 dant, the stoker usually piles an unnecessary quantity of fuel upon his fire, and this 

 has the effect of reducing the heat, and of producing dense volumes of black smoke. 

 Where coal is scarce and dear, as in Cornwall, careful stoking leads to an almost 

 entire absence of smoke. A small quantity of coal is placed in front of the fire at a 

 time ; here it undergoes a coking process, the volatile carbon passing over the heated 

 coal is burnt, and no visible smoke escapes. When the coal is thoroughly coked, it is 

 shovelled in over the fire, and a fresh portion of coal is placed in front, to undergo 

 the same process. 



Prevention of Smoke. The attention of the legislature has been directed to this 

 nuisance, and sundry Acts have been passed to regulate and reduce the evil. The 

 following extract from the 'Act to Amend the Smoke Nuisance Abatement (Metro- 

 polis) Act' (16 & 17 Viet. cap. cxviii.) August 20, 1853, should have every attention 

 from manufacturers : 



' Freni and after the 1st day of August 1854, every furnace employed or to be 

 employed in the metropolis in the working of engines by steam, and every furnace 

 employed or to be employed in any mill, factory, printing-house, dye-house, iron- 

 foundry, glass-house, distillery, brew-house, sugar-refinery, bake-house, gas-works, 

 water-works, or other buildings used for the purpose of trade or manufacture within 

 the metropolis (although a steam-engine be not used or employed therein), shall in 

 all cases be constructed or altered so as to consume or burn the smoke arising from 

 such furnace ; and if any person shall, after the 1st day of August 1854, within the 

 metropolis, use any such furnace which shall not be constructed so as to consume or 

 burn its own smoke, or shall so negligently use any such furnace, as that the smoke 

 arising therefrom shall not bo effectually consumed or burnt, or shall carry on any 

 trade or business which shall occasion any noxious or offensive effluvia, or otherwise 

 annoy the neighbourhood or inhabitants, without using the best practical means for 

 preventing or counteracting such smoke or other annoyance, every person so 

 offending, being the owner or occupier of the premises, or being a foreman or other 



