406 PRINCIPLES OF CHEMISTRY 



CHAPTER X 



SODIUM CHLORIDE BERTHOLLET's LAWS HYDROCHLORIC ACID 



Ix the preceding chapters we have become acquainted with the most 

 important properties of the four elements, hydrogen, oxygen, nitrogen, 

 and carbon. They are sometimes termed the organogens, because they 

 enter into the composition of organic substances. Their mutual com- 

 binations may serve as types for all other chemical compounds that is, 

 they present the same atomic relations (types, forms, or grades of 

 combinations) as those in which the other elements also combine 

 together. 



Hydrogen, HH, or, in general, HR. 



Water, H 2 O, H 2 R. 



Ammonia, H 3 X, ,, H 3 R. 



Marsh gas, H 4 C, ,, H 4 R. 



One, two, three, and four atoms of hydrogen enter into these 

 molecules for one atom of another element. Xo compounds of one 

 atom of oxygen with three or four atoms of hydrogen are known ; hence 

 the atom of oxygen is without certain properties which are found in 

 the atoms of carbon and nitrogen. 



The faculty of an element to form a compound of definite composi- 

 tion with hydrogen (or an element analogous to it) gives the possibility 

 of foretelling the composition of many other of its compounds. Thus, 

 if we know that an element, M, combines with hydrogen, forming HM, 

 and not forming H 2 M, H 3 M, H n M m , then we must conclude, on the 

 basis of the law of substitution, that this element will give compounds 

 M 2 O, M 3 N, MHO, MH 3 C, tfcc. Chlorine is an example of this kind. 

 If we know that another element, R, like oxygen, gives with hydrogen 

 a molecule, H 2 R, then we may expect that it will form compounds like 

 hydrogen peroxide, or the metallic oxides, or carbonic anhydride, or 

 carbonic oxide, and others. Sulphur is an instance of this kind. 

 Hence the elements may be classified according to their resemblance 

 to hydrogen, oxygen, nitrogen, and carbon, and in conformity with 

 this analogy it is possible to foretell, if not the properties (for example, 



