Human Physiology. p/ 



some gases to the extent of 400 to 600 times its own bulk. A 

 pint of water absorbs, holds within itself, 600 pints of gas. 

 Atmospheric air is taken up by water to a large extent, so that 

 fishes can breathe it. They drown as quickly in water without 

 air, as we do in water. Gases, also, adhere to solids, forming, 

 it would seem, an atmosphere round each atom or molecule. 

 Powdered platinum condenses 800 times its volume of oxygen. 

 Charcoal takes up great quantities of gases, hence its use in 

 purifying the ventilators of sewers, and to form respirators. It 

 is by the strong adhesion of air to metals that iron filings and 

 needles swim on the surface of water. 



The phenomenon of dissolving matter is very remarkable. 

 A crystal of common salt is very hard that is, the forces of 

 attraction and repulsion hold its atoms rigidly in their places, 

 but each atom of salt has a stronger affinity for atoms of water 

 than for its own brother atoms. The moment water atoms 

 come near, even in a moist atmosphere, the salt atoms lose 

 their attraction for each other. A force seems annihilated. 

 Drive off the water by heat and the salt atoms take up their 

 old relations. This is one of many thousands of things I am 

 not able to account for; but chemistry is full of the play of 

 such forces. 



I put some iron filings in a bottle with water and a little 

 sulphuric acid. Iron atoms hold to each other with immense 

 force, but they will leave each other instantly to join atoms of 

 oxygen. They lay hold of the oxygen atoms in the water, 

 which also leave their atoms of hydrogen. The hydrogen 

 rises in bubbles, and may be used to fill a balloon ; or, bring a 

 match, set it on fire that is, make it join more oxygen and 

 become water. The iron has become an oxyde, but only for 

 an instant, for it is seized by the sulphuric acid, and you have 

 but to evaporate the water to get crystals of sulphate of iron 

 copperas which, uniting with tannic acid, another crysta 1 

 dissolved in water, makes the ink with which I write. 



G 



