~ 128 MM, Fer anp Fremy. 
for cleaving ; but they have the colour and the hardness, &c., 
and we have prepared large masses in which crystals have been 
found which leave absolutely nothing to be desired. Besides, we 
are still studying this interesting question, and without doubt 
we shall soon arrive at a perfect result in every point of view. 
The second part of our investigation, 7.¢., that on the crystallized 
silicates, will serve to demonstrate the influence of the fluorides as 
crystallizing agents. By submitting to heat, during a determined 
time, a mixture of fluoride of aluminum and vitrifiable earth, we 
noticed that, by the mutual reaction of the two bodies, fluoride 
of silicium is evolved, and we obtain a crystallized body which 
seems to be disthene—that is to say, a silicate of alumina. It 
appears under the form of acicular double refracting crystals, 
which extinguish the light obliquely towards their edges. ‘These 
crystals afforded on analysis the following results :— 
Vitrifiable earth, * “ : ° : 47°65 
Alumina, - 4 = ‘ " 51°85 
Loss, ; . : . ; 0:50 
It is about the same as for disthene, or its varieties, trebolite, 
bucholzite and bamlite, and sillimanite. 
By operating in a certain manner, and by heating to a high 
temperature a mixture of alumina and fluoride of barium, we 
obtained prismatic needles several centimetres in length. Their 
analysis afforded :— 
Vitrifiable earth, . ; é : , 34:32 
Baryta, : ° . ‘ ° 35°04 
Alumina, . 4 : : : . 30°37 
M. Jannettez has ascertained that these long prisms are often 
composed of four blades with parallel faces forming the surfaces 
of a hollow prism ; they extinguish the light under the microscope, 
or rather they let the obscurity persist between two crossed 
prisms. They may be cut at angles of 60° 42’ and 119°. 
In the course of the reaction which generates the crystallized 
double silicate just described, some corundum is formed. These 
bodies are the results of the following changes :— 
By heating the mixture of alumina and fluoride of barium, 
fluoride of aluminum and barium is formed. 
*This term is doubtless used as a synonym of silica.—Eds. 
