Mr. M. M. Pattison Muir on Chemical Classification. 187 



machine, and whicli vdW be found described in Goodeve's 

 ^ Elements of Meclianism/ 3rd edit, page QQ, 



It is obvious that by an extension of the same principle an 

 apparatus could be made to give the tracing of a combination 

 of three or more waves. To do this, however, the mechanical 

 arrangements must be much better than in the comparatively 

 rough instrument I have exhibited. 



XXIV. On Chemical Classification. By M. M. Pattison Muir, 

 F.JR.S.E., Assistant Lecturer on Chemistry^ The Owens Col- 

 lege, Manchester. 



[Continued from p. 99.] 



18. TT^ROM what has been said in the preceding paragraphs, 

 -L it is apparent that to fix the valency of an element is 

 a most difficult task. I think it is also apparent that at pre- 

 sent it is only from gaseous compounds that we can look for 

 much help in this task. So difficult is it to determine the 

 valency of an elementary atom that many chemists have been 

 inclined to regard each element as possessed of several valen- 

 cies varying with the compounds which the element forms. 

 Thus carbon in carbonous oxide would be regarded as a dyad, 

 and in carbonic oxide or in marsh-gas as a tetrad. Other chemists 

 have regarded the power of combining with a definite number 

 of hydrogen, chlorine, &c. atoms as an essential and unalter- 

 able property of the elementary atom. To say that the atom 

 of an element is now divalent, now trivalent, to attempt to 

 explain the differences between compounds by means of the 

 hypothesis of "var}dng valency" is, as Lothar Meyer has 

 well pointed out, to vouchsafe no explanation at all. What is 

 required from the upholders of the " varying- valency " theory 

 is a reference of the different valencies exhibited by one and 

 the same element to some distinct and definite cause. The 

 question at issue is most distinctly stated in Meyer's work 

 already referred to (2nd edit. pp. 244, 245), " Is every elemen- 

 tary atom capable of combining with a certain definite number 

 of other atoms ? and is this power solely dependent upon the 

 nature of the matter composing the atom, or is it also condi- 

 tioned by outward circumstances ? " 



The general facts, some of which have been enumerated in 

 paragraphs 15, 16, and 17, appear to me to justify one in con- 

 cluding that, probably, the capacity of saturation of each atom 

 is an essential and definite property of the atom, dependent 

 upon the nature of the matter composing the atom, but that 

 this power is capable of being modified or conditioned by ex- 

 traneous influences. Whether these extraneous influences are 



