ON DIMORPHOUS BODIES. 177 
The seventh group has been inserted on the authority of 
Kohler, whose paper may be consulted with advantage, and some 
doubt may be supposed still to hang over the isomorphism of 
silica and chabasie, though on this similarity of form I have 
elsewhere* founded an explanation of certain optical phenomena 
observed by sir David Brewster in some varieties of chabasie, as 
well as of certain differences in chemical constitution, which 
specimens from different localities have been found to present. 
23. Attempts have not been wanting toreconcile some of thedis- Are these 
cordant formule exhibited by the above isomorphous -groups, formule re- 
but hitherto without much success. Thus Dr. Clarke has en- "UC" 
deavouredt to reconcile the formule for anhydrous sulphate of 
soda (NaO + SO,) and permanganate of baryta (BaO + Mn,0,), 
forming the sixth group in the above table by supposing 
1° That the equivalent of sodium is double of that generally 
received or Na, soda being Na, and an equivalent of the anhy- 
drous sulphate of soda Na,O,+ 8,O¢. 
2° That the acids combine directly with the metals and not 
with their oxides, and consequently that the rational formule 
for the two salts in question are respectively (representing Na, 
by Na) Na+S,0, and Ba+Mn,O, or Na+S and Ba+Mn 
in which state the formule correspond, and the isomorphism of 
the two salts becomes intelligible. 
_ The first of these hypotheses must be rejected, I believe for 
reasons which will find their natural place in a succeeding 
paragraph (26), the second is so completely opposed to all ex- 
‘perimental evidence that chemists could hardly be expected to 
regard it with a favourable eye even though the first hypothesis 
to which it serves as a sequel were not deemed inadmissible. 
_ Great violence to received opinions must not be offered for the 
_explanationof a single apparent anomaly. Each groupin thetable 
would probably require one or more specific hypotheses to recon- 
cile the formule of the several substances which compose it, and 
_ these hypotheses, as appears in the following section, might often 
os conflicting, showing that we are still far from a glimpse of the 
truth. 
_ Why should it be thought necessary to reconcile the formule 
| of isomorphous bodies, except that, carried away by the beauty 
| of the doctrine of Mitscherlich, we have generalized too hastily ? 
| Ifthe same substance may crystallize in two or more different 
* Lond. and Edinb. Phil. Mag., vol. ix. p. 166. 
+ Records of Science. 
VOL, VI. 1837. N 
