152 ATTRACTION. 



(g.) Mere mechanical mixtures are separated by mechanical means ; 

 muddy water becomes clear by filtration and by repose, which have 

 no effect upon salt water. 



(h.) Energetic chemical action produces an entire change of prop- 

 erties. Oxygen and hydrogen have no resemblance to water or to 

 each other ; nitric acid and potassa none to salt petre ; muriatic acid 

 and soda none to common salt ; potassium and oxygen none to po- 

 tassa and so on, in a thousand cases more. Inert substances pro- 

 duce active compounds, as in sulphuric acid; active principles inert 

 compounds as in sulphate of pot?ssa ; compounds containing an en- 

 ergetic principle or principles, retain a degree of activity, sometimes 

 great, as nitrate of silver and many oilier metallic salts, and arseniate 

 of potassa ; inert principles produce inert compounds, as in borate of 

 magnesia, and in a word, there is g''eat variety in the results, so that 

 they cannot be predicted, and can be learned from experiment only. 



(i.) Colors are produced, and different colors by different propor- 

 tions of the same materials. The metallic oxides and salts, red lead, 

 oxide of mercury, the chromates of lead, natural and artificial, and 

 the two sulphwets of mercury and of arsenic, are examples. 



Jj.) Colors are destroyed. Chlorine destroys nearly all colors, 

 the sulphurous acid many. 



(k.) The specific gravity is changed, and generally increased. 

 Compounds of ammonia and the acid gases are precipitated in the 

 form of solid sails ; but some of the metallic alloys are lighter than 

 the mean specific gravity of the metals combined ;* and some gaseous 

 combinations form other gaseous compounds that are lighter, but in 

 general aeriform bodies by combining, undergo condensation.^ 



(/.) Temperature, or sensible heat, is changed. It is increased, as 

 when alcohol and water, sulphuric acid and water, oxygen and com- 

 bustibles, sulphur and metals, iodine and phosphorus, are united. 



It is diminished, as by solution and by all freezing mixtures. 



(m.) The form of bodies is changed. 



Solids become fluid, as in the freezing mixtures ; also Glauber's 

 salts and nitrate of ammonia rubbed together. Webster. 



Fluids become solid, as water in slaked lime, and in nearly all 

 crystals. 



Solution of strong muriate of lime, decomposed by strong sulphu- 

 ric acid is precipitated solid ; most acids by combining w r ith different 

 bases produce solids, provided water is removed by evaporation. 



Gases become liquid. Oxygen and hydrogen form water. 



* The constituent particles may have approximated and the integrant particles 

 receded, so that the fact involves no impossibility. 



t In olefiant gas, the elements in a state of freedom would occupy four volumes 1 

 instead of one. 



