EVOLUTION THE RESULT OF CHEMICAL FORCES. 93 



gas, or oxygen and any of the minerals, a permanent solid at all 

 ordinary temperatures. The chemical union of hydrogen and 

 nitrogen is ammonia, of hydrogen and chlorine is hydrochloric 

 acid, of hydrogen and sulphur is hydrosulphuric acid, and so on 

 through a long list, all suffocating and destructive gases. ISTow 

 all the compounds of hydrogen with any other element except 

 oxygen, when they do freeze, which is only at very low temper- 

 atures, turn into solids that are heavier than their liquids and 

 sink in them as fast as formed. So likewise all the compounds 

 of oxygen with any other base except hydrogen, follow the gen- 

 eral law of contraction in bulk through all stages of cooling. 

 But water when cooling, as is well known, commences to expand 

 from a few degrees above freezing, and the ice that is formed 

 always floats on the surface of the waters. 



I have stood on the brink of the great surging fountain of 

 liquid lava in the volcano of Kilauea in the Sandwich Islands, 

 and have seen it quiet down and freeze over like a lake of 

 water, turning from glowing red to black. After a few moments, 

 in some spot or along a crack, the crust would begin to sink 

 downward, the edges of the huge blocks would turn up, and 

 then disappear in the liquid, which commenced again to leap in 

 columns and dash against the shore. 



If bodies of water froze over and the crust sank in them as 

 the lava in this caldron of melted silica, then all freezing lakes 

 and rivers and seas would turn into solid ice. The inevitable 

 final result would be that all the water of the world would accu- 

 mulate in solid frozen masses in the regions of ice-forming 

 latitudes. 



Water is in all respects an exceptional product. It is excep- 

 tional in its abundance, in its being a liquid at ordinary tempera- 

 tures, in its perfectly neutral qualities, in its solvent and hydra- 

 ting properties, in its constant evaporation from liquid and even 

 solid conditions, in its frozen form being a non-conductor of heat, 

 and above all in its expansion in freezing so that ice remains 

 always on the surface. On these exceptional facts, and especially 

 on the last, depend not only the well being but the possibility of 

 life on the earth. 



