404 T. S. Hunt on Chemical Classifications. 



ammonia and the acid minus the same elements ; and if we would 

 be consistent with the view which makes C„H 5 (C 4 H 5 Liebig), 



and NH 4 , radicals equivalent to H, we must equally admit 

 H Q N -O and C„EL -O to the same rank, for they are as really 



equivalents of H the atom of hydrogen. 



Thus do the compound radicals come to be mere mathematical 

 expressions ; the only value which can ever be attached to them 

 is that which belongs to an irreducible expression in an algebraic 

 formula. Understood in this way as representing the equivalent 

 of certain other elements, they may be conveniently introduced 



in our chemical formulas. 



M 



celebrated hypothesis ; had he seen the necessity of such substi- 



N-H 



tutes for O as — 5 — at the same time with NH 2 , he would have 



never given the latter a rank which could imply its existence even 

 in combination. Although the elements which in an ammoni- 



m resented by NH 4 , there is no more rea- 

 son for supposing a separate existence to the elements denoted by 

 the expression than to the kindred formulas NH 2 — O and N — O 



— — — — — ^^ — 



for the conception of the one violating, as it does, the laws of 

 molecular constitution, is no less monstrous than the other. 



To represent then, the etherids and amids of oxalic acid, in 

 accordance with the compound radical theory, we have 



1. Oxalic acid, C^H^O,. 



2. Oxalovinic acid, C 2 (H(C o II 5 ))0 4 . 



3. Oxalic ether, C 2 (C 2 HJ 2 4 . 



4. Oxamic acid, C 3 (H(NH 2 - 0)0 4 . 



5. Oxamid, C 2 (NH„ -0)„0 4 . 



6. Oxamethane, C 2 ((C 2 H 5 )(NH 2 -0))0 4 . 



The introduction of Liebig's system seems to have been almost 

 a necessary event in the progress of chemical philosophy; it 

 was a view which, as discovery advanced, very naturally pre- 

 sented itself to minds impressed with the notion of dualism, in- 

 culcated as one of the first principles of the science. A saline 

 substance is regarded as a binary combination of an oxyd and an 

 acid, or a metal and a radical, in which these two actually exist 

 as such, and the analogies between compounds, like chlorid of 

 potassium and salammoniac, are such that if we regard one as a 

 binary combination of Na with CI, the other must be viewed as 

 formed by the union of NH 4 with CI. It has however been 

 shown that the elements thus replacing hydrogen or a metal, have 

 not only not a necessary, but sometimes not even a possible, ex- 

 istence, and that all we can infer from such substitutions, is that 

 those expressions represent an equivalent amount of the forces 

 which are necessary to preserve the integrity of the complex 

 molecule. Chlorine, as known to us, does not exist in common 

 salt, for from the combining volume of the gas, it appears that in 



