The Outline of Science 



application in silver-plating and the like. A brass spoon, let us 

 say, is immersed by a wire in a solution of a silver salt (say. ;i 

 solution of silver cyanide* in potassium cyanide) , and the spoon is 

 the one pole the cathode. A sheet of silver is the other pole the 

 anode. A weak electric current is passed through the fluid, and 

 cations of silver are then deposited on the brass spoon, which be- 

 comes a silver-plated spoon. 



Mr. C. T. Kingzett, in his Popular Chemical Dictionary, says 

 of chemical changes : 



All articles of food and clothing; the materials of which 

 our houses and buildings are constructed and which are 

 needed for their decoration or repair ; every art and every in- 

 dustry all depend essentially for their production or 

 activity upon chemical changes as realised in nature or made 

 by man to serve human purposes. The same is true of the 

 production and decay of animals and vegetable matters, as 

 also the process by which they are broken up and the 

 resulting products made available in. their turn as food for 

 new life. These chemical changes constitute a sort of adapta- 

 tion of matter to environment, and in a sense are acts of 

 creation, as every such change produces products which, 

 although related, are quite distinct in character and in prop- 

 erties from the original substances which give rise to them 

 when subjected to the required influences. Thus, in a very 

 literal sense, all matter which, as will be seen in other places, 

 appears to be essentially one in nature is actuated by a spirit 

 of life, being susceptible to change when the environment is 

 appropriate. 



Chemical Change 



Chemistry is concerned with the different kinds of matter in 

 the world and with the changes which they produce by interaction, 

 If a bar of iron is heated it becomes longer, but it returns to its 

 original length when cooled. We call this a physical change, for 

 the iron remained iron from first to last. But when a piece of iron 



