THE 
LONDON, EDINBURGH anv DUBLIN 
PHILOSOPHICAL MAGAZINE 
AND 
JOURNAL OF SCIENCE. 
[FOURTH SERIES.} 
JUNE 1860. 
LIV. Crystalline Form not necessarily an indication of definite 
Chemical Composition ; or, on the possible Variation of Con- 
stitution in a mineral Species independent of the Phenomena of 
Isomorphism. By Jostau P. Cooke, Jun., A.A.S., Professor 
of Chemistry and Mineralogy in Harvard College, United 
States of America *, 
i ey a memoir presented to-the American Academy of Arts and 
Sciences in September 1855+, I described two new com- 
pounds of zinc and antimony, which I named stibiobizincyle and 
stibiotrizincyle, on account of their analogy in composition to 
the metallic radicals of organic chemistry. The symbols of these 
compounds are Sb Zn? and Sb Zn°; and they are distinguished 
by the high perfection of their crystalline forms, the last beng 
still further characterized by a most remarkable property of de- 
composing water quite rapidly at 100°C. I stated in the same 
memoir that crystals of these two compounds could be obtained, 
containing proportions of zine and antimony differing very widely 
from those required by the law of definite proportions; and I also 
traced out the relation between the composition of the crystals, 
and that of the menstruum in which they are formed. It is my 
object in the present paper to consider the bearing of these facts, 
already fully described, on the idea of mineral species, and to 
offer a few suggestions which I hope may be of service in de- 
termining the true chemical formule of many minerals, and thus 
in simplifying the science of mineralogy. But in order to render 
myself intelligible, it will be necessary to recapitulate very briefly 
the facts in question, referring to the original memoir for the full 
details. 
* Communicated by the Author. 
+ Transactions of the American Academy of Arts and Sciences, New 
Series, vol. v. p. 337. 
Phil, Mag.8. 4. Vol. 19, No, 129, June 1860. 2K 
