CHEMICAL SCIENCE. 213 



bining proportion of hydrogen, were chemically inseparable from one 

 another, they were really tantamount to one atom only of hydrogen, and 

 as a matter of fact were always employed by Berzelius as representing 

 the single chemical atom of hydrogen, or its smallest actual combining 

 proportion. Distinguishing thus between the physical atom and the com- 

 bining proportion, Berzelius's recognition of the truth that equal volumes 

 of the elementary gases contain an equal number of atoms was utterly 

 barren. But, identifying the physical atom with the combining propor- 

 tion, Gerhardt's recognition, or rather establishment, of the broader truth 

 that equal volumes of all gases, elementary and compound, containing th'j 

 same number of atoms, has been in the highest degree prolific. From 

 Gerhardt's division of volatile bodies into a majority whose recognized 

 molecules corresponded respectively with four volumes of vapor, and 

 a minority, whose recognized molecules corresponded respectively with 

 but two volumes, and from his proposal, in conjunction with Laurent, to 

 double the molecular weights of these last, so as to make the molecules 

 of all volatile bodies, simple and compound, correspond each with four 

 volumes of vapor, must, I conceive, be traced the development by himself 

 and others of the mature views of chemical philosophy which now 

 prevail. With every respect f >r other authorities, I cannot join with 

 them in regarding the indication of Gerhardt's system as an imperfect 

 return, and its remarkable maturation in these recent days as a more 

 complete return, to the notions of Berzelius. It is true that the ele- 

 mentary weights now employed, with the exception of those for ?ome 

 half-dr.zen metals, are identical with the atomic weights of Berzelius ; but 

 so different are they from his combining weights, that fully |- of all known 

 compounds have to be expressed by formulas entirely different from his, 

 namely, all those bodies, with but a very few exceptions, into which 

 hydrogen, fluorine, chlorine, bromine, iodine, nitrogen, phosphorus, ar- 

 senic, boron, and the metals lithium, sodium, potassium, silver, and gold, 

 enter as constituents. Fully admitting that the new system of atomic 

 weights, as it now exists, is the joint product of many minds, fully ad- 

 mitting that it owes its present general acceptance chiefly to the intro- 

 duction of the water type by Williamson during Gerhardt's lifetime, and 

 the recognition of diatomic metals by Wurtz, and Cannizzaro, after his 

 decease, and fully admitting, moreover, that some of Gerhardt's steps in 

 the development of his unitary system were decidedly, though perhaps 

 excusably, retrograde, I yet look upon him as being the great founder of 

 that modern chemical philosophy, on the general spread of which I have 

 already ventured to congratulate the members of the Section. Prior to 

 the time of Gerhardt's, the selection of molecular weights for different 

 bodies, elementary or compound, had been almost a matter of hazard. 



nena, he first es- 

 the considerations 

 logically depend. 



Relying upon these principles he established his classification of the non- 

 metallic elements into monhydrides, represented by chlorine, dihy- 

 drides, represented by oxygen, tc-rhydrides, represented by nitrogen, 

 &c. ; and relying upon the same principles, but with a greatly increased 

 knowledge of phenomena, later chemists have given to his method a de- 

 velopment and unity, more ('specially as regards the metallic elements, 

 which have secured for the new system the impregnable and acknowledged 



