of Chemical Operations. 421 



pound radical " to the portion of matter represented by C 2 H 4 

 or C 2 H 5 , for instance, we do not express any other idea. The 

 compound radical represents to us a portion of matter which 

 in the series of phenomena under consideration is transported 

 integrally from one combination into another, although it may, 

 in other circumstances, be decomposed into simpler elements. 

 " Compound radical," or " simple relative weight/'' are there- 

 fore one and the same thing. Here, again, is a matter of 

 words. 



We may add that the substitution of hypothesis a for hypothe- 

 sis a 2 is not fundamental. If, supposing that Sir B. C. Brodie had 

 not written his two memoirs, it had been shown that the bodies, 

 so called, of uneven atomicity contain hydrogen, and correspond 

 to the general formula HR 2 or H 2 R 4 , immediately our existing 

 notation would be transformed, except for the use of Greek 

 letters, into that of Sir B. 0. Brodie, without any alteration 

 in the general system, unless it were the important discovery 

 of the compound nature of a series of bodies hitherto con- 

 sidered as elementary. 



To set against this* there is in the existing notation a series 

 of hypothetical considerations for the expression of fine iso- 

 mers, which Sir B. C. Brodie rejects. Thus, when we ex- 

 press the isomeric relations of aldehyde, acetylenic alcohol, 

 and oxide of ethylene by the formula 



C=}H 3 C=}H 2 C=}H 2 



I „ II 1=0" 



c zzS- o" c_ „_ H J" 2 



we make a hypothesis on the mode of grouping these atoms 

 considered as metaphysical entities. 



It is the same when we try to account for the differences 

 existing between isomers such as salicylic, oxybenzoic, and 

 paraoxybenzoic acids, and explain them by the place occu- 

 pied in relation to each other by the groups OH and C0 2 H 

 and the benzol-group C 6 H 6 . 



We will return presently to this hypothetical part of our 

 notation. Let us pause for a moment on the part common to 

 the existing notation and the notation of Sir B. C. Brodie, and 

 see if, in fact, the hypothesis a, setting aside the difficulty 

 caused by the necessity of considering as compounds a mass 

 of simple weights, offers the advantages over the hypothesis a 2 

 which Sir B. C. Brodie asserts. According to him, a hypo- 

 thesis is acceptable when it accounts for all the known facts. 

 Of two hypotheses which equally account for all the facts, that 



