256 Rev. J. B. Emmet t on the [Apkil, 



changed ; oxygen gas is a powerful supporter of combustion ; 

 hydrogen gas is highly inflammable ; their compound is equally 

 destitute of either of these properties ; water may be con- 

 gealed, but at the lowest temperature hitherto produced, each 

 element retains its gaseous state. 



Into a vessel of carbonic acid gas introduce a stream ofammo- 

 niacal gas ; the gases will ultimately disappear, and a white 

 crystallized solid will result, which retains the properties of the 

 ammonia in a mild form, but none of those which distinguish the 

 acid. 



If dry nitrous gas and oxygen gas be mixed in proper propor- 

 tions, the volume is reduced to one half; the gases, which were 

 invisible, assume a deep-orange colour ; each was destitute of 

 acid properties ; the compound is a powerful acid. 



By combination, solids sometimes become liquid or gaseous. 

 Mix together a solid amalgam of zinc with one of bismuth ; the 

 mixture becomes fluid. Burn a piece of charcoal in a confined 

 portion of oxygen gas ; the charcoal disappears, and carbonic 

 acid gas is produced : the charcoal, therefore, by combination 

 assumes a gaseous state. Similarly, mix dry muriate of lime 

 and snow at a very low temperature ; they rapidly become 

 liquid. 



The colours of bodies are often changed ; dissolve peroxide 

 of iron in sulphuric acid ; into one portion drop solution of 

 prussiate of potash, an intense blue precipitate is formed ; into 

 another portion pour solution of hydrosulphuret of potash, the 

 precipitate is black ; into a third pour subcarbonate of potash, 

 and a yellowish-red precipitate is obtained ; with arsenite of 

 potash, a dull yellow. 



The forces which produce chemical changes often act with 

 extreme violence ; place a thin slice ot phosphorus upon a grain 

 or two of hyperoxymuriate of potash; give it a gentle blow with 

 a hammer, and a most violent detonation will follow. 



During combination, a change of temperature takes place. 

 Mix four parts of dry lime with one of water ; the water loses its 

 fluidity, for thelimeremainsdry, and much heat is excited. Intro- 

 duce phosphorus, pulverized antimony, or bismuth into chlorine 

 gas ; the gas will be absorbed, and brilliant combustion ensues ; and 

 in all cases, if the volume be reduced, heat is excited; if increased, 

 or if solids become liquid, or liquids, gaseous, cold is produced. 

 Again, bodies which are susceptible of chemical union, combine 

 only in certain definite proportions ; thus in water, the weight 

 of oxygen has to that of the hydrogen a constant ratio. If 

 bodies can combine in two, three, or more different proportions, 

 the ratio of the quantities of one of the elements to a given 

 weight of the other will be as the numbers, 1, 2, 3, &c. The 

 force of chemical attraction is not the same in all bodies of the 

 same class, as is manifest from the various cases of simple and 

 compound decomposition. These, and all other chemical changes 



