516 M. Deville on the Artificial Formation of certain Minerals. 



by an ulterior reaction of aqueous vapour this is changed into 

 crystals which are somewhat larger and more perfect. 



Hydrochloric acid also exercises a very curious reaction on 

 amorphous titanic acid, changing it into very small crystals which 

 resemble anatase or rutile. They are very lustrous, and have a 

 bluish colour, like natural anatase. This blue colour arises from 

 a partial reduction of titanic acid ; for when this body was treated 

 in a reducing atmosphere by gaseous hydrochloric acid, small 

 crystals were obtained of a deep indigo-blue colour, the analysis 

 of which showed that they were a new oxide of titanium, 



Ti 3 5 =Ti0 2 ,Ti 2 3 , 



Artificial rutile may also readily be obtained by the following 

 method devised by Deville in conjunction with Caron. When a 

 mixture of titanic acid and protoxide of tin is made, a titanate is 

 formed at a red heat, which silica decomposes, forming a silicate 

 and crystallized titanic acid. The operation is effected by heat- 

 ing to redness in an earthen crucible titanic acid along with oxide 

 of tin and a little sand. A gangue is formed rich in tin, and in 

 which ar*e imbedded crystals of rutile 5 or 6 millims. in length. 

 Their form is that of native rutile ; they are pure and colour- 

 less if the materials are so, but they usually contain a trace of 

 iron or manganese, which give them the colour of native rutile. 



• In the same manner Deville* has studied the formation of other 

 minerals. 



Magnetite. — Magnetic oxide of iron was prepared by heating 

 protoxide of iron in a slow current of hydrochloric acid gas. 

 Protochloride of iron was formed, but no water. The crystals 

 remaining in the tray were regular octahedra, and were found 

 on analysis to have the formula Fe 3 O 4 . The protoxide of iron 

 was prepared by Debray's method of heating sesquioxide of iron 

 in a mixture of equal volumes of carbonic acid and carbonic oxide 



Periclase. — When calcined magnesia was heated in a slow cur- 

 rent of hydrochloric acid gas, it was transformed without any loss 

 into small crystals of periclase, which were sometimes white, 

 sometimes greenish, and occasionally yellow from the presence 

 of iron. Their form is the regular octahedron, and when pro- 

 duced at a very high temperature they are of considerable size. 

 Chloride of magnesium in vapour is also decomposed by water, 

 forming transparent octahedra of periclase. 



Martite. — When a mixture of calcined magnesia and sesqui- 

 oxide of iron was heated in a slow regular current of hydrochloric 

 acid, two distinct substances were produced ; one of them was 



• Compies Rendus, July 29, 1861. 



