Mineralogy and Geology. 271 
be but variable mixtures. of albite and anorthite. Such crystalline 
mixtures are very common; thus in the alums, aluminium, iron an 
chromium, potassium and ammonium, may replace one another in indefi- 
nite proportions, and the hydrated sulphates of copper and magnesian 
metals, are obtained in similar mixtures. Heintz has shown by frac- 
tional precipitation, that there are mixtures of homologous fatty acids, 
which cannot be separated by crystallization, and have hitherto been 
regarded as distinct acids. he autho 
Il. Mrneratocy anp Gro ocy. 
1. Notice of von Kobell’s paper on Series of Isomorphous and Homeo- 
morphous Forms, published in Schweigger’s Jour., vol. Ixiv, p. 410; b 
J.D. Dana.—In_ this early paper of von Kobell, published in 18382, 
(but which we had not the privilege of consulting till receiving quite 
tecently a translation from Mr. G. J. Brush, now in Munich,). the sub- 
ject of the relations of form among minerals of the Dimetric and also 
¢ Hexagonal System is presented in a similar manner as regards 
the general principle, to that of the writer in the last volume of this 
Journal. Von Kobell aims to show that in the dimetric and hexagonal 
ms as in the monometric, there are many species related in form 
related in composition. After some details with reference 
n@ comparison of dimetric species differing widely in composition, 
oa the similarity of form, of Meionite and Wernerite ; Copper 
ide yrites, and Braunite, he afterwards adds Nagyagite, Corneous Lead, 
Zircon, Rutile, native Calomel. Thus relations among the dimetric 
<Pecies are rought out, very similar to those presented by the writer 
in his recent paper. 
Von Kobell next takes up the Hexagonal System, and shows the 
wots between the Corundum group (including, as first shown by 
'lscherlich, Specular Iron and Ilmenite) and the Calcite group. The 
relation of the Calcite and Corundum groups is shown by comparing 
ER of Calcite with —4R of Specular Iron; and the rhombohedron of 
Copper Mica 68° 41’ is shown to be near —2R of Specular Iron; while 
*gain Red Silver Ore is observed to be near Calcite in angle, the arsen- 
Tiety giving the angle 107° 40’ to 107° 36’. Von Kobell also 
i remarks that ‘** other hexagonal species may be brought into sim- 
ar series, if differences of 14 degrees be neglected. The series of 
and corundum are united by bery! with the series of apatite 
.. Pytomorphite ; magnetic pyrites and chlorite both have pyramids 
"th the. basal angle 120°.” ‘The fact of a relation in form among 
