20 



THE WORLD WE LIVE IN 



and table salt, are simple, inasmuch as they contain only two or 

 three elements; but the greater number of compounds found in 

 nature are very complex. The chemist uses several symbols to 

 designate the binding together of elements into compounds. 

 Several symbols together are known as a formula. For example, 

 H 2 is the formula for water and indicates that two parts of hy- 

 drogen combine with oxygen in a definite proportion by volume. 



. t1 , A chemical com- 



m blood Serum 



in sect v/fcxter* 



sodium. 



magnesium 

 Calcium J? 

 potassiunv 



chlorine 



SO* 



CO3 , 



bromine 3 



50.59 



3.73 



1.2, 



55.27 



7M 



r.2\ 

 49 



39. 



45.- 



1<2. 



._ socCiu m 



magnesium 

 —daidium 

 •potassium 



.-Chlorine^ 



£o 3 



PzOs 



According to analysis, scientists have found that the per- 

 centages of chemical substances in sea water are quite similar to 

 those found in the blood serum (after Osborne). 



pound is a combina- 

 tion of two or more 

 elements in which 

 each of the elements 

 loses the character- 

 istics which distin- 

 guished it. For ex- 

 ample, if fine iron 

 filings and flowers 

 of sulphur are 

 mixed, each element 

 will retain its own 

 peculiar properties, 

 can still be recog- 

 nized, and can be 

 easily separated by 

 means of a magnet 

 which will attract 

 the iron. But, if the 



mixture is heated in a test tube, several important changes in the 

 mixture will take place. A solid black substance is obtained 

 which is not attracted by a magnet. The elements can no longer 

 be separated by mechanical means. This black substance is a 

 compound called iron sulphide. It has several properties quite 

 different from those of either the iron or the sulphur. Rocks, 

 humus, organic food substances, and the bodies of plants and 

 animals are all composed of chemical compounds. 



Professor H. F. Osborne of Columbia University has pointed 

 out that the chemical substances found in sea water correspond 



