and Chemical Composition of Minerals. 
Peroxide of Iron, 
Sulphate of Magnesia, 
Muriate of Magnesia, 
Water of Crystallisation, 
0.1 grain 
100.0 
Mr Phillips considers the Iron and the Muriate of Magnesia 
as merely accidental ; but as I could not avoid doubting the ac- 
curacy either of the analysis or of this opinion, I transmitted 
several specimens of the salt to M. Berzelius, I am not yet 
able, however, to communicate his analysis. 
In January 1817, I discovered the differences in the optical 
structure of the Apophyllites of Faroe and IJton These diffe- 
rences were so striking, as to entitle us to consider the two sub- 
stances as distinct minerals. M. Berzelius has made a very 
accurate analysis of the apophyllite of Uton ; but I have not 
yet received from him his analysis of the Faroe specimens. The 
composition of the Uton crystals is KS G -f- 8CS 3 ; and he con- 
jectures that the Faroe ones may be composed of KS 5 -f 8CS 3 , 
or KS 6 -p 6CS 2 , with the same or a different dose of water. 
A series of specimens which I received as Acetate of Copper , 
furnished me in the year 1817 with a still more striking proof 
of the connexion between the optical structure and the chemical 
composition of bodies. The green Acetate had twp axes of 
double refraction, and also the faculty of absorbing polarised 
light ; while the blue Acetate had only one axis, and was entire- 
ly destitute of the absorbent property *f*. In a large mass of 
crystals of acetate of copper which Dr Ure had the goodness to 
present to me in December 1817, the green and the blue acetate 
had been formed from the same solution, the blue crystals being 
on the outside of the mass. This circumstance seemed to ren- 
der it highly probable that they were the same substance, not- 
withstanding the difference in their optical structure, and I ac- 
cordingly requested Dr Ure to analyse them. The results of the 
analysis were as follows, the blue crystals being acetate of copper 
and lime, and the green crystals the bin-acetate of copper. 
-f- See Fh.iL Tran v. 1818, p. 2 II 
* See Ellin . PhiL Journal, vol. i. p, j. 
