128 MM. Feil and Fkemy. 



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, i.e., 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 verifiable 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 : — 



Verifiable earth,* .... 47*65 



Alumina, ..... 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 : — 



Verifiable earth, ..... 34-32 

 Baryta, . . . . .35-04 



Alumina, ...... 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. 



