ATTRACTION. 153 



Gases become solid. Acid gases and ammonia precipitate solid 

 salts, (vide k.) 



Solids become gas. Several ammoniaeal salts, properly decom- 

 posed, are converted into aeriform bodies ; this is true, particularly of 

 the nitrate and muriate of ammonia. 



Fluids become gas. Water decomposed by galvanism with gold 

 or platina wires affords oxygen and hydrogen gases in mixture.* 



(n.) Jl very minute division of matter is effected by chemical union. 

 It is much more minute than any mechanical means can produce ; ni- 

 trate of silver discovers the slightest trace of muriatic acid : so am- 

 monia detects any salt of copper ; hydriodic acid platinum ; recent 

 muriate of tin and green sulphate of iron discover gold. 



(o.) Cohesion resists chemical action. Therefore as a prelim- 

 inary it is diminished, by the mechanical operations of pounding, 

 rasping, grinding, &tc. and by previous chemical operations, as when 

 caustic potash is fused with refractory gems and stones, to prepare 

 them for solution in acids. Marble in lumps, dissolves slowly in acids, 

 but in powder rapidly, so of salt, sugar, &-c. 



(p.) Affinity is not universal. Water does not dissolve siliceous 

 sand, nor resins, nor oil, nor clay ; these bodies may be mixed with 

 water by mechanical agitation, but they will^separate again by repose, 

 or by filtration or other mechanical means. 



(q.) No body, elementary or compound, is without affinities. Sili- 

 ceous sand unaffected by water, is dissolved by caustic potash ; resin 

 by alcohol, oil by alkali, common clay, in part, pure argil entirely, by 

 sulphuric acid. 



(r.) Solution is only a particular case or mode of chemical action 

 and union. It takes place generally, between solids and fluids ; but 

 is also predicable of the other forms of matter ; gases dissolve solids 

 and fluids, and these in turn absorb gases. 



(s.) Solution is generally promoted by heat. In the cold, 4oz. 

 of water do not dissolve 3oz. of sulphate of soda, but heat enables 

 the whole to be readily dissolved. Henry. 



(t.) The solubility of different substances, in the same fluid, is very 

 different. Joz. sulphate of ammonia, Joz. sulphate of soda, T Voz. 

 of sulphate of potash, and j^ of sulphate of lime, are dissolved in 

 loz. distilled water. Id. 



(u.) Heat generally promotes chemical action; as is commonly said, 

 and in most cases truly, by diminishing the power of cohesion, as is 

 seen in the solutions of solids ; but this explanation would hardly apply 

 to the explosion of gunpowder, and of fulminating powders. Some- 

 times cold brings on chemical action ; sea water, containing muriate 



* Many important chemical events depend on condensation or evolution of gases ; 

 explosions are often produced by the latter. 



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