CHEMISTRY 



1294 



CHEMISTRY 



teenth century, concerned itself with the rela- 

 tion between medicine and chemistry. The 

 body, said these early chemists, is made up of 

 various chemicals and then each proceeded to 

 make for himself a list of these body sub- 

 stances. If one of the chemicals was present 

 in excess, they argued, disease was certain to 

 result, and many illnesses were labeled as 

 growing out of too much or too little of some 

 one substance. Paracelsus, the greatest of these 

 doctor-chemists, really effected many cures and 

 made discoveries that are of the utmost value 

 to modern pharmacy. But men knew too little 

 of anatomy and physiology, as well as of chem- 

 istry itself, to carry this really helpful phase of 

 the science very far. 



Finally there arose men who realized that if 

 this study of substances and their composition 

 was to become a real science it must be car- 

 ried on for its own sake and not by reason of 

 its relation to gold-making or to healing. From 

 that time on, progress was comparatively rapid. 

 Robert Boyle, for instance, who lived in the 

 seventeenth century, held as theory much that 

 has now been proven fact. Thus he knew much 

 about the doctrine of elements, so fundamental 

 to the science, and announced the difference 

 between a chemical compound and a mixture 

 (see below, Chemical Compounds). Other 

 men who later added greatly to the growth of 

 the science, and whose work is discussed under 

 their names in these volumes, were Bunsen, 

 Sir Humphry Davy and Remsen. Other mod- 

 ern chemists have added vastly to the stores 

 of knowledge left by these men, but they have 

 altered little the main principles laid down by 

 them. Thus the central doctrines of elements, 

 substances which cannot be decomposed, have 

 never been disturbed. 



Elements. When an electric current is passed 

 through water, two gases, oxygen and hydrogen, 

 are obtained, which are substances entirely 

 different from water. If we try by any means 

 known to science to-day to obtain either from 

 oxygen or from hydrogen any simpler substance 

 we will not succeed. Neither will we succeed if 

 we try to decompose iron, or gold, or carbon. 

 Such substances which cannot be decomposed 

 into other simpler substances or cannot be 

 transformed into one another are named ele- 

 ments. Elements are substances whose mole- 

 cules contain only one kind of atoms. Oxygen 

 contains nothing else but oxygen; gold con- 

 tains nothing but gold. Up to the present 

 chemists have found that there are in nature 

 eighty-three elements. All the thousands and 



thousands of other materials that are in ' the 

 world are either chemical compounds of these 

 eighty-three elements, or mixtures made up of 

 more than one element or compound. Air, for 

 instance, is a mixture of the two elements oxy- 

 gen and nitrogen; salt is a chemical compound 

 of the elements sodium and chlorine ; and milk 

 is a mixture of several chemical compounds. 



The following list contains the name of each 

 element, its symbol (see subhead below, 

 Chemical Symbols), and its atomic weight: 



