46 H. ROSE ON THE COMBINATIONS OF THE 
be detected in the elements, manganese is a radical just as 
chlorine is; both can combine with oxygen, and in the highest 
stages of oxidation there is a very considerable analogy evident 
between the two. Sulphur and chromium, which can replace 
each other, differ in like manner, while several sulphate and 
chromate salts are isomorphous ; whence it results that a substi- 
tution of sulphur and of chromium by chlorine, in certain combi- 
nations, is likewise possible. 
If, however, a substitution of oxygen by chlorine cannot be 
admitted, a replacement of hydrogen by chlorine is far less pro- 
bable. But this very substitution, as is well known, is the 
most prominent point in the theory advanced by Dumas; and a 
great number of cases seem to render it probable, although in 
numerous other cases such a substitution does not occur. 
No view in modern times has, perhaps, been so stimulating 
and fruitful as that of Dumas on the substitution of hydrogen 
by chlorine. We are indebted to it for a vast series of the most 
excellent researches in organic chemistry, which, without this 
excitement, would probably not have been undertaken. But all 
these labours do not prove such a substitution beyond contro- 
versy, if we except the most recent discovery of De la Provostaye 
of the isomorphism between oxamethane and chloroxamethane*. 
Although there may exist a great number of substitutions 
which are not distinguished by isomorphism, yet without con- 
tradiction this is the most certain indication of a true substi- 
tution. After the discovery, therefore, of De la Provostaye, no 
objection could be made to the substitution of hydrogen by 
chlorine, if this discovery were confirmed. But from the de- 
scription of the forms of the crystals, the isomorphism cannot 
be confidently relied upon. 
Should, however, the substitution of hydrogen by chlorine be 
irrefutably proved by several examples, by the isomorphism of 
compounds which these elements form, then indeed we must 
arrive at the conviction that in complex combinations the group- 
ing of the atoms only, and not the different chemical nature of 
the elements, necessitates analogy in properties. 
The same conclusions as are drawn from the combination 
of the sulphate of the chloride of sulphur with ammonia, like- 
wise follow from the combination of the carbonate of the 
* Annales de Chimie et de Physique, t. xxv. p. 322 ; and Philosophical Maga- 
zine for May 1841, p. 372. 
