220 J. D. Dana on the Isomorphism and , 
Art. XXV.—On the Isomorphism and Atomic. Volume at some 
Minerals ; by James D. Dana 
oe perused recent statements by Prof. G. Rose respecting 
some anomalous cases of isomorphism, and also having remarked 
that ie “dlidiakeally unlike minerals chrysoberyl and chrysolite 
were essentially alike in form, I was led to a farther search for 
such singular anomalies among minerals in order to elicit the prin- 
ciple upon which they depend. ‘The results of the investigation 
have proved interesting beyond what was expected, and are de- 
tailed in the following pages 
Before proceeding with them, the facts observed by Prof. Rose 
should re mentioned. He points out the relations of bismuth, 
arsenic and some other metals,+ and also shows that specular iron 
and alumina are isomorphous with them, as seen in the following 
ta 
. 
Osmium, R: R=84°52’ | Bismuth, R: R=87°40! 
Iridium, 84 52 | Palladium, undetermined. 
Arsenic, 85 04 
Tellurium, 86 57 rundum (alumina) Al R:R=86 4 
_ Antimony, 87 35 Specular i iron (Fe 85 58 
Titanic iron (#e, Pi) 85 59 
Prof. Rose also gives the following parallel groups of iso- 
morphs.{ 
1. Form that of Cale Spar. 
R:R 
Cale spar and isomorphs RG 105° — 107940" 
b. Nitrate of soda Naf 106 33 
ee | Dark red silver ore + 8AgS+SbS3 108 18 
Light red silver ore 3AgS+AsS3 107 36 
2. Form that of Arragonite (dimorph with the preceding). 
M:M 
Arragonite, — lead ore, de. RO 116° —118°80’ 
5 Nitrate of potas 119 
ce. Bournonite 8(€u, Pb)S+SbS3 115 16 
Many examples of this kind of isomorphism have come to light 
in the course of the research ; and moreover an ae is 
at hand in the relations of atomic volume—the same principle 
mage to by Kopp for explaining the cases of ordinary is0- 
mor 
* The atomic numbers adopted in the body of the opines’, table have in a few 
instances ion slightly changed, since this article in such canes , the 
numbers employed i in the follo owing noses will be found i in pomp a to the table. 
t e rhombohedral metals. natsb. der Kénigl. Preuss. Akad. der Wissen- 
sok a 
» AL 
+ In an article “on a remarkable analogy of form between certain sulphur 
en salts,” Monatsbericht der Kéingl. 9g Akad. d. Wissenschaften zu eri, 
Jan., 1849, p. 18. Pogg. Annal, lexvi, p. 2 
