444 MODERN CHEMISTRY. 



minuteness of the molecules of matter, as rendered certain 

 by experiment, can be expressed to the understanding by 

 numbers only. We have mentioned some instances already ; 

 such as the detection of a millionth part of Iodine in solution. 

 In Faraday's experiments on the optical properties of Gold 

 solutions, he found that a strong ruby tint was given to a 

 fluid by a proportion of gold not exceeding the half-millionth 

 part in weight. Examples of the same kind are endless, and 

 furnished by every part of nature, organic and inorganic. 

 But none approach in wonder those recently derived from 

 the spectrum analysis. By experiments conclusive in their 

 method and results, Bunsen was able to detect 7U u(J o w( fh part 

 of a grain of Lithium in a compound ; while of Sodium, the 

 metal of common salt, the delicacy of the indication by the 

 yellow line traversing the spectrum, was such that the 

 i8o oou ooot* 1 P ar ^ f a g ram could be made clearly perceptible 

 in its effects. 



We must not stop here to relate the ingenious methods 

 through which these conclusions were obtained, or to give 

 other examples to the same effect. They all show that in 

 the primitive constitution and multiform changes of material 

 bodies, nature works with molecules or ultimate parts of 

 indescribable minuteness ; which minuteness we may con- 

 clude from the phenomena to be absolutely essential to the 

 functions they fulfill. Equally essential does it appear to be, 

 that these molecules should tend to unite under certain 

 definite forms ; and, where dissimilar in kind, under certain 

 fixed proportions of number or weight. In this law, if we 

 may so term it, lies the explanation, both of the uniformity 

 and of the diversities pervading every part of the natural world. 

 The whole system of Chemistry rests upon this foundation ; 

 and is guided in its researches and inductions, in its nomen- 

 clature and symbols, by a reference to this great principle. 

 The doctrine of definite proportions is further the bond of 



