911 
The specifie gravity of the erystallised MnSiO, is die= 3,716 at 
25° C.; for the glass :dye— 3,48. 
With artificial Mn S/O, no reliable meltingpoint could be found ; 
the compound became gradually darker by decomposition. With a 
natural Mn SiO,, a tephroite of Sparta (N./.), we found with 
thermoelement / 1) successively : 
E.M.F. at the meltingpoint: 13185 M.V., if the furnace-gradient was 
60 M.V. per minute. 
12991 M.V., if the furnace-gradient was 
40 M.V. per minute. 
Mean: 13088 M.V.+ 9 M.V. (uncorr.) 
which, after correction, corresponds to: 1292° + 8° C. The melting- 
point is „ot sharp; for the artificial, pure silicate it probably will 
‚be higher, in agreement with the temperature mentioned by Dorrtnc- 
KEL (1323° C... 
The melted and again solidified artificial Mn,S’O, differed rather 
appreciably from the natural tephroite used; while the latter had 
the refractive indices: », = 1,709, and n, = 1,693, the birefringence 
being: 0,016, — the indices of the melted artificial product appeared 
both to be greater than 1,739. Whether this solidified product repre- 
sents another modification of the substance, or an impure and par- 
tially decomposed tephroite, can now hardly be said; the specific 
weight of the artificial, melted and again solidified Mn,S7O, is: 
dy = 4,043 at 25° C. 
For the purpose of comparison we investigated also a beautifully 
crystallised preparation of Goreru'), which was obtained by the 
interaction of MnCl, and S/O,, under co-operation of introduced 
water-vapour. This rhodonite consisted of optically negative, often 
irregularly extinguishing, triclinic needles; 7, was greater than 1,739 
and n, was 1,728; birefringence about: 0,013. The corresponding 
tephroite had the shape of greyish-brown, flat, metallic looking 
needles, which probably were of rhombic symmetry, and whose 
refractive indices appeared both to be greater than 1,739. 
§ 1t. If now we summarise the results of these and former 
determinations, we can give the following survey : 
1) GorGEU, loc. cit. 
Proceedings Royal Acad. Amsterdam. Vol. XVIII. 
