268 Mr. M. M. Pattison Muir on Chemical Classification. 



stituted by the elements which are arranged in the following 

 tables. The elements are placed in the ascending order of 

 their atomic weights ; and over each is placed a fignre repre- 

 senting its yalency^ so far as that has been with probability 

 ascertained. 



Section I. 



1. 2. .3. 4. 3. 2. 1. 



Li Be B C N F 



Section 11. 



1. 2. 3. 4. 3. 2. 1. 



Na Mg Al Si P S CI 



Considerations such as those which were mentioned con- 

 cerning the members of the nitrogen group may lead ns to 

 more determinate views concerning the valency of groups of 

 elements. The eight elements belonging to the group in 

 question form analogous oxides (72X3 O5), some of which are 

 more stable than others. Does it not appear very probable 

 that the eight elements are really possessed of equal valency, 

 but that the intensity, or the amount, of the chemical force 

 exercised by each is different ? We must never forget that 

 the valency of an element and the chemical force exerted by 

 that element are, in all probability, very different quantities. 



If this view be adopted, the members of the nitrogen group 

 must be regarded as pentads, and such compounds as P CI3, 

 Bi CI3, &c. as unsaturated compounds. Whether this be 

 granted or denied, it is, I think, evident that the study of the 

 general characters and analogies of compounds in the light 

 of Mendelejeff's periodic law is calculated to throw consider- 

 able light on the general question of unsaturated compounds. 

 (See par. 16.) 



MendelejefF has shown how the elements may be arranged 

 in groups and in series in conformity with the gradual 

 increase in their atomic weights. These groups may be 

 again subdivided, and thus striking analogies and contrasts 

 brought out betw^een the members of the various groups. 

 The remarks which I have already made illustrate the manner 

 in which such divisions may be carried out. If the power of 

 forming oxides, chlorides, hydrates, kc. be a periodic func- 

 tion of the atomic weights of the elements, we shall, when 

 the nature of this function has been more studied, be in pos- 

 session of an instrument whereby we may be able to arrive at 

 a knowledge of the chemical composition or structure of 

 groups of compounds. I have already attempted to show 

 how a study of the general chemical reactions, and of the 

 physical properties, of compounds, aids us in determining the 



