Chemistry and Physics. 111 
remaining in the furnace eight consecutive days. The crystals thus 
produced were octahedrons truncated upon the twelve edges; some of 
hem three or four millimeters in the side : they were transparent, of 
great lustre and of a more less marked rose color. The angles measured 
rr last mentioned compounds correspond almost perfectly, that of the 
ean being 25-2, that of the latter 25-1. Chromite of manganese, 
"203, MnO, was obtained by igniting together oxyd of chromium, 
ra of manganese and boric acid. e crystals were regular octa- 
herd’. of 2 Semi-metallic iron gray color, of density 4:87, and of a 
ardness Sufficient to scratch quartz. Chromite of zinc, Cr2Os, ZnO, 
oe Procured in the same manner and obtained in the form of small, 
dene tiant Tegular octahedrons of a greenish black color, and o 
foura. 5°309.at 1] C. The atomic volumes of the chromites were 
taba higher than those of the aluminites, that of chromite 
n 
i . ‘ 
en 287, of chromite of iron 28°3. Ferrite of zinc was ob- 
ined in the form of small black brilliant octahedrons, of density 5-132. 
Is atomic volume is 29-3. ‘i 
par he formation and properties of the artificial cymophane were de- 
tibed by the author in his first memoir. By repeating the experi- 
te with the addition of carbonate of lime to the mixture of alumina, 
£iucing and b : ' 
i oe at 12C. The crystalline form was found to correspond 
acing with the determinations of Descloizeaux made with the natural 
in, Fs man 
razil and the Ural. “The author next describes two new com- 
insole eOUS aspect and very high lustre ; its 
ee In water but sanilp-pihiaia in acids. Peridot, 
obtained by fusing together silica, magnesia and boric 
slightly Were several: millimeters in length, : 
deeply plows their form was an oct 
: my truncated upon é preeeee 
