CHEMISTRY OF THE NINETEENTH CENTURY. 607 



his life in danger. The value to the world of these researches is that 

 they made known the first anczsthetic that came into use in effecting 

 surgical operations without pain. It is also the only quite safe one, and 

 as such is still very much used in minor surgical operations, particularly 

 by dentists. Davy's researches extended to the several combina- 

 tions of oxygen and nitrogen, and were the means of giving chemists 

 more exact knowledge of these compounds than had hitherto been 

 obtained. 



But the greatest of all Davy's chemical discoveries was that of the 

 decomposition of the alkalies, soda and potash. This discovery was 

 made in 1807 by help of a galvanic battery of about 250 couples. Davy 

 first tried to decompose aqueous solutions of the alkalies, but the result 

 was only the disengagement of hydrogen gas at one pole and oxygen 

 at the other. It then occurred to him to pass the current through 

 potash in a state of fusion. In this case he found some combustible 

 substance was separated : he could not, however, obtain this substance 

 until he had modified the form of the experiment. He then found at 

 the negative pole small globules of a high metallic lustre. Some of 

 these burnt with a bright flame almost as soon as they formed ; but 

 others remained, and became tarnished by a white film which formed 

 on their surfaces. The lustrous matter was no other than the metallic 

 base of potash, the existence of which had before been suspected. This 

 metal received the name of potassium, and a few days after its discovery 

 Davy succeeded in similarly isolating from soda the metal since called 

 sodium. 



Potassium and sodium are very light and very soft metals, in colour 

 and lustre not unlike silver. Their surfaces are instantly tarnished by 

 exposure to air, the oxygen of the air rapidly combining with the 

 metal. A piece of either metal placed in contact with water decom- 

 poses the latter with evolution of hydrogen gas, and .the result is a 

 solution of the corresponding alkali. The hydrogen is inflamed by 

 the heat attending the combination when the action takes place in 

 the air. When a small piece of either metal is confined under water, 

 a violent action ensues, and the hydrogen produced may be collected 

 in appropriate vessels. In order to moderate the violence of the 

 action in this experiment, Davy previously united the metal to mer- 

 cury, and he found that the resulting amalgam permitted the hydrogen 

 gas, liberated by the action of the potassium and sodium, to be con- 

 veniently collected and measured. The mercury is left pure and un- 

 changed, as the only products are hydrogen, and a solution of the alkali, 

 potash or soda, as the case may be. 



The experiments of Lavoisier and others had proved that the con- 

 stituents of water were oxygen and hydrogen. In these experiments 

 the synthetical process only could be exhibited ; that is to say, water 

 was put together from its elements. But in 1800 Nicholson and 

 Carlisle discovered a mode of effecting the inverse operation ; that is 



