SOD 



SOL 



ous ; stamens 6 ; ovarium 3-celled ; fruit 

 a berry. 



SMOKE. Smoke consists of the un- 

 consumed gaseous elements of any body, 

 and, consequently, arises from imperfect 

 combustion. 



SNOW. The frozen visible vapour 

 composing clouds. K flake of snow ex- 

 hibits a beautiful display of minute crys- 

 tals, often possessing the greatest variety 

 of forms. Tlie production of snow offers 

 the most simple case of the precipitation 

 of water from the atmosphere. 



SNOW LINE. That limit of elevation 

 in every latitude at which the air attains 

 the temperature of freezing water. The 

 line of perpetual congelation is, of course, 

 the summer limit. 



SNOW, RED. The colouring matter 

 of this substance appears to be an alga- 

 ceous plant, named jjro^ococcMS nivalis. 

 Agardh's definition of Protococcus is 

 merely, *' plants with aggregated, not 

 mucous globules." To this Greville 

 added, " globules containing granules 

 seated on a transparent gelatinous 

 mass." 



SNOWDON ROCKS. One of the 

 subordinate divisions of the Cambrian 

 Group of Rocks, of many colours and 

 textures, varying from fragmentary to 

 the finest roofing-slate. 



SOAP. A compound, in definite pro- 

 portions, of certain principles in oils, 

 fats, or resin, with a salifiable base. 

 Hard soap is made of soda and fatty or 

 resinous matters ; soft soap is made of 

 caustic potash and acid oil or fat. 



SOAPSTONE. Steatite. A mineral 

 consisting of silicate of alumina and 

 magnesia, and named from its resem- 

 blance to mottled soap and from its unc- 

 tuous feel. 



SO'BOLES. The botanical term for 

 the creeping stem, or slender stem of cer- 

 tain plants, which creeps horizontally 

 below the surface of the earth, emitting 

 roots and new plants at intervals, as in 

 triticum repens. 



SODA. The protoxide of sodium ; an 

 alkali procured from the ashes of marine 

 plants ; formerly called the mineral 

 alkali, from its being found native, 

 under the name of natron, in mineral 

 seams or crusts. 



• SODA-WATER. A solution of the 

 bicarbonate of soda in water, when an 

 additional quantity of carbonic acid has 

 been forcibly combined with it. 



SO'DALITE. A mineral substance 

 consisting of a silicate of soda and alu- 

 S06 



mina, found in Greenland, in Mount 

 Vesuvius, and in Siberia. 



SODIUM. Natrium. A white metal 

 with the aspect of silver, soft and mal- 

 leable at 32°, quite liquid at 194°, and 

 volatilized at a red heat. Davy obtained 

 this metal by the voltaic decomposition 

 of soda, immediately after the discovery 

 of potassium. 



SOIL, VEGETABLE. The external 

 thin layer of earth in which plants grow, 

 composed of fragments of minerals, vege- 

 tables, and animals, reduced to a great 

 degree of tenuity. 



SOL. The Sun; a globe, 1,300,000 

 times greater than the earth, and situated 

 at a mean distance of 94| millions of 

 miles from the earth. 



SOLANA'CEiE. The Nightshade tribe 

 of dicotyledonous plants. Herbaceous 

 plants or shrubs, with leaves alternate; 

 flowers monopetalous, regular; stamens 

 inserted into the corolla; ovarium 2- 

 celled ; fruit succulent. 



SOLA'NO. The name given to a hot 

 wind which blows in Spain and Portugal. 

 It is a modified sirocco. 



SOLAR DAY. The interval between 

 two transits of the sun over the meri- 

 dian. It is longer than the sidereal day ; 

 for if the sun move slowly eastward, and 

 if it be on the meridian with a certain 

 star to-day, then to-morrow, when that 

 star comes on the meridian, the sun 

 will be a little to the eastward, or not 

 yet on the meridian : that is, the solar 

 day is not quite completed in a sidereal 

 day. 



SOLAR PHOSPHORUS. A general 

 term for those substances which, after 

 exposure to light, exhibit phosphorescent 

 properties, as Canton's phosphorus, &c. 



SOLAR SYSTEM. The Solar System 

 comprises the sun as a centre, and thirty 

 other bodies, which revolve round him 

 in regular periods and at various dis- 

 tances. See Planet. 



SOLDER. A simple or mixed metal, 

 by means of which metallic bodies can 

 be firmly united with each other. Hard 

 solders are ductile, malleabie, and are 

 usually prepared of the same metal with 

 that which is to be soldered, with the 

 addition of some other ; soft solders melt 

 readily, are partly brittle, and therefore 

 not malleable; bismuth is much used in 

 the composition of soft solders, from its 

 capability of forming with several metals 

 compounds of remarkable fusibility. 



SOLDERING. The process of uniting 

 the surfaces of metals, by the interven- 



