176 GENERAL SCIENCE 



Both may be disposed of by treating the water with small 

 amounts of substances that give off chlorine when in water. 

 One such compound is known as calcium hypochlorite, and 

 in an impure form it is sold in cans as " bleaching powder." 

 Its uses as a disinfectant, for destroying offensive odors from 

 decaying organic matter, and for bleaching cotton goods, 

 all are the result of this oxidizing process that follows the 

 chemical change between the chlorine and water. 



Among the items of household supplies there are few where 

 greater inconvenience would be caused in doing" without 

 them than in the case of friction matches. People camping 

 out are at times painfully aware of this. Yet it is less than 

 a hundred years since they have been used. The heads of 

 safety matches consist of some substance rich in oxygen, 

 such as potassium chlorate, mixed with antimony sulphide 

 and glue. The surface on which the safety match heads are 

 to be rubbed is a mixture of glue, red phosphorus, and some 

 material such as powdered glass to largely increase the fric- 

 tion. Aside from the danger of fire from the accidental 

 ignition of yellow phosphorus when used in matches, its 

 deadly effects upon the workmen in match factories are such 

 as to condemn its use. 



SUMMARY 



Where chemical changes occur it is believed that the quantity of 

 matter involved in the change remains the same. However, the ap- 

 pearance of entirely different characteristics in the matter after the 

 change warrants the statement that new substances have been formed, 

 and that the original substances have wholly or in part ceased to exist. 



Elements in chemistry are believed to be made up of atoms of like 

 kind, while compounds contain unlike atoms. 



Both heat and solution are aids to chemical action, and in many cases 

 are necessary to bring it about. Plants of microscopic size are agents 

 in bringing about decay in dead organic matter, and in causing other 

 chemical changes. Lifeless substances known as enzymes promote 

 chemical changes in the digestion of foods and elsewhere. 



