214 ELEMENTARY GENERAL SCIENCE CHAP. 



heat until no more sulphur burns away, and do this three or 

 or four times. Weigh the product so obtained, and then 

 examine it carefully. Try to separate the sulphur and copper 

 by washing, and try to dissolve the sulphur out by carbon 

 disulphide. You will now find that you cannot separate the 

 two components, neither can you distinguish the individual 

 particles. 



The substance so formed is a compound of copper and sulphur, 

 so that during the heating a change has taken place, with the 

 formation of a new substance with properties of its own. This 

 is an example of a chemical change the result of chemical 

 action. The new substance is a chemical compound. If you 

 have taken the weight carefully you will have also found that 

 100 parts of copper form, roughly, 125 parts of the compound, 

 that is, unite with 25 of sulphur, and the result does not depend 

 on the actual weight of copper and sulphur used, all excess 

 of sulphur over this being always burnt away. We thus find 

 the following differences between a mixture and a compound : 



MIXTURE. In a mixture the components exist side by 

 side and can be separated by simple mechanical methods. 

 The ingredients may be present in any proportions, and the 

 properties of the mixture are intermediate between those 

 of the constituents. 



COMPOUND. In a compound the components cannot be 

 separated by the simple means available in the case of 

 mixtures. The properties of the compound are quite diifer- 

 ent from those of the constituents, and these constituents 

 are always present in certain definite proportions which for 

 each compound are invariable. 



In all cases of chemical action it is most important to remember 

 that the total weight remains absolutely unchanged, that is, the 

 total weight of all the products is exactly equal to the total 

 weight of all the components forming these products. 



CHIEF POINTS OF CHAPTER XIV. 



Physical Changes are those in which the composition of the body 

 experiencing the change remains unaltered. The science concerned 

 with these changes is called Physics . 



Chemical Changes are those which result in the formation of new 

 substances with new properties. The study of such changes is 

 called Chemistry. 



Chemical Elements are kinds of matter which can, by no known 



