A Sketch of the Laws of Chemical Combination. 313 



covered with respect to them, form one of the most important parts of 

 Chemistry. The following is a summary of them : — 



1. Tlie composition of bodies is fixed and invariable. Thus water is 

 ahcays formed by 1 part of hydrogen, and 8 of oxygen : sulphuric acid, 

 by 16 of sulphur, and 24 of oxygen j and so ou. This law was first esta- 

 blished by Wenzel, a German chemist, about the year 1777. 



2. There is a constant numerical relation between the proportions in 

 which all bodies combine with each other. The numbers expressing the 

 proportions in which any two bodies unite with a i>iven quantity of a third 

 substance, express also the proportions in which these bodies are disposed 

 to combine with one another. Thus 6 parts of carbon, or 8 of oxygen, 

 will combine with 1 of hydrogen, or with 35"42 of chlorine ; and on the 

 other hand, 6 parts of carbon will combine with 8 of oxygen, and 1 of 

 hydrogen with 35*42 of chlorine. These numbers are therefore termed 

 the combining or chemical equivalents of the respective bodies ; and they 

 have been found to correspond exactly with the electro-chenticnl e*[\n\'^Qi\ts, 

 deduced by Faraday from the comparative quantities of different substances 

 which are decomposed by the same amount of electricity. The law of 

 chemical equivalents does not apply to elementary substances only, since 

 compound bodies also have their combining proportions, which are always 

 expressed by the sum of those of their constituents. The discovery of this 

 law is })rincipally due to Dalton. 



3. When one body unites with another in two or more proportions, their 

 relative quantities bear to each other a very simple ratio ; being in almost 

 every instance either as 1 to 1, 2, 3, &c. ; or as 1 to \\, 2, 2|, 3, &c. 

 The progress of chemical research is rapidly reducing the number of the 

 less simple kinds of compounds, by showing that they may often be con- 

 sidered as combinations of two of the former class. Thus the red oxide of 

 lead, and the black oxide of iron are now viewed somewhat in tlie light of 

 salts, formed by the nnion of the peroxides of these metals with their 

 protoxides : and the oxides of manganese afford tivo, if not three, instances 

 of this kind of combination. We owe the first announcement of this law 

 to Dalton, and its subsequent verification and extension, principally to 

 Berzolius. 



Tlie atomic theory of Dalton, which is based upon the foregoing laws, 

 supposes that masses of matter arc composed of atoms or indinisible par- 

 ticles, which differ in weight in different substances, and unite definitely 

 with each other. The number exi)ressiTig the proportions in which bodies 

 unite, must likewise on this view indicate the relative weights of the atoms j 

 and accordingly these numbers are often called atomic weights. Thus, as 

 water is composed of eight parts of oxygen, and one of hydrogen, it fol- 

 lows, on the supposition of its consisting of one atom of each element, that 

 an atom of oxygen must be eight times heavier than one of hydrogen. 

 This view, however, being entirely theoretical, must not be confounded 



