SCIENTIFIC TERMS. 147 



Safety Lamp. See page 76. 



Suit, chloride of soda. Of this there are two kinds, sea salt and rock 

 salt. Sea-salt is obtained by evaporating sea-water, which when 

 done sufficiently the salt will form in crystals. Rock-salt is 

 obtained from mines in various parts of the world. England sup- 

 plies it very plentifully. 



Salts, the combination of any base with an acid. 



Sapphire, a precious stone of a blue colour. The finest sapphires come 

 from the East Indies, although remarkably beautiful ones have been 

 found in Scotland. This is the hardest of all the gems, with the 

 exception of the diamond and the ruby. 



Sardonyx, a precious stone of the agate kind. 



Sebacic-acid, an acid procured from fat, whence it takes its name. 



Selenite, a species of gypsum or plaster of Paris. 



Silicum, the metallic base of silica or flint. 



Silver, a well known metal possessing great tenacity, ductility, and 

 malleability. It has very little affinity for oxygen, and is of so 

 indestructible a nature, that it may be kept in a state of fluidity 

 through intense heat for a long time with but a trifling loss of weight. 



Siphon, a bent tube used for the purpose of drawing off liquors. 

 See page 48. 



Snow, particles of water frozen in falling. See page 55. 



Soda, the mineral alkali. See page 23. 



Sodium t the metallic base of soda. See page 23. 



Spectrum, an oblong image of light made by a prism. See page 31. 



Stalactites, spars in the form of icicles found hanging from the roofs of 

 caverns, &c. 



Statics, a branch of physico-mathematical science, which considers 

 weight or gravity, and the motion of bodies resulting therefrom. 



Steel, iron combined with carbon. 



Steel-yard, the most ancient and universal instrument used for the 

 purpose of ascertaining the weight of bodies. The Jews, Greeks, 

 and Romans used it, and it is in general use throughout Asia at the 

 present day. It is in fact a balance of unequal arms, and depends 

 on the principle of the lever of the first kind for its action. 



Strontium, the metallic base of the earth strontites. 



Sublimation, a process whereby certain substances are volatilized bv 

 heat, and again condensed by cold into a solid form. Flowers of 

 sulphur are made in this way. 



Sulphur, a well known simple substance, found in combination with 

 metals and otherwise. See page 21. Sulphurous and Sulphuric 

 acids are formed through the affinity of sulphur for oxygen. Sul- 

 phur, in combination with another substance, forms a sulphuret ; 

 sulphurous and sulphuric acids form in combination Sulphites and 

 Sulphates. 



Synthesis, the composition of any body from its original parts. 



Syringe- Condensing, an instrument used for the purpose of charging 

 the ball of an air-gun. See page 40. 



Telescope, an instrument for viewing distant bodies. By a combina- 

 tion of lenses the object is seen under a larger angle than with the 

 naked eye, and its apparent magnitude proportionately increased. 

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