44 CHEMISTRY. 



this is the case with sulphur, phosphorus, and carbon far- 

 ther on. Oxygen lias a great attraction for hydrogen, 

 and is continually uniting with it, on every hand produc- 



ing water. 



Some substances can be made to unite with each other 

 only under the most extraordinary circumstances. This is 

 the case with oxygen and nitrogen. No degree of heat to 

 which we may subject them together can force them to 

 unite. Lightning does it to a small extent, as it shoots 

 through the atmosphere, forming nitric acid. And the pow- 

 er of this and many other analogous compounds consists, at 

 least for the most part, in the looseness of the affinity which 

 holds their constituents together. They destroy by falling 

 to pieces, their elements uniting with other substances for 

 which they have an affinity. This is the explanation of the 

 action of all caustics they do not eat and themselves re- 

 main whole, but they are decomposed in the destruction 

 which they cause. So, too, the efficacy of gunpowder de- 

 pends upon looseness of affinity in the nitre, and the conse- 

 quent readiness with which it furnishes one of its elements, 

 oxygen. 



39. Providence Seen in Affinity. The various degrees of 

 affinity between different substances are adjusted by the 

 Creator, as all other forces in nature are, with an obvious 

 reference to the comfort and welfare of man. Take, for ex- 

 ample, the different degrees of affinity which oxygen has 

 for hydrogen and nitrogen. With hydrogen it is uniting 

 every where and continually to form water. This is done, 

 as you will see, in all ordinary combustion. Now if oxy- 

 gen united with nitrogen with the same ease if the heat 

 of ordinary combustion could cause them to combine, form- 

 ing nitric anhydride with the great abundance of these 

 gases in the air the most disastrous effects would result 

 every where. So, also, if sulphur had the same degree of 



