( 249 j 
The highest temperature to which IT have submitted my materials, 
was acquired by blowing into an open Bunsen flame with an artificial 
blowpipe-apparatus. ) The very small splinters of the mineral can 
be thus brought to a very high temperature probably to 2000° Jh 
A platinum wire of '/, mM. at once melted in it. 
As investigation material for disthene, I used the blue variety 
(find-place Gängerhausen). Before the heating, the index was 1.73 
and after it (I experimented in the way just described), it sank to 1.62; 
so far below that of sillimanite. 
If disthene had actually turned into sillimanite, it should have 
kept its index (1.68); sillimanite submitted to the same temperature, 
not changing its index in the least. So this shows that heating does 
not turn disthene into sillimanite. i 
To try whether 1300’ would bring the index to 1.68, I pro- 
ceeded thus: 
I took several earthen mugs, put in each a piece of disthene together 
with other metals of which the melting temperatures are known, 
heated the metals to a temperature that would keep them for a moment 
in melting condition and thus obtaining constant temperatures, I could 
fix the indices of disthene, which proved to be gradually lower. Lower 
than 1.62, it could not be reduced, in spite of continued heating. 
On the subjoined diagram, the different temperatures and indices are 
stated. On one of the axes are the indices, on the other the degrees 
from hundred to hundred. The line starting from 1.68, running 
parallel with the axis of the temperatures, represents the direction 
of the index of sillimanite. That line remained constant. The broken 
line marks the direction of the index of disthene. They cut each other, 
as will be seen, at about 1250? C. 
The deviation in silver is probably caused, either by the not absolutely 
accurate melting temperature or by a slight inaccuracy in the index. 
The reason of it is probably that we have a mixture of materials 
of which one more and more prevails; what pleads for this, is the 
erowing intransparency of disthene, a fact noticed also by VurNapsky. 
At a degree of 1.62 disthene grows entirely opaque, consequently, 
it has got entirely amalgamated with the other material. 
Of course this argument is open to discussion, but up to now, I 
have not been able to find a better one. This phenomenon, may 
be of some practical usefulness in making maxim-pyrometers, since 
it proves that a constant index may be obtained by heating to a certain 
temperature. 
1) To be had at Atrmann’s in Berlin, 
