as a constituent of many Rocks. 109 



was always noted, as also a high index of refraction. These 

 characters strongly indicated the identity of this mineral with 

 allanite, and a qualitative chemical analysis, made by Dr. W. 

 ~F. Hillebrand in the Denver laboratory of the U. S. Geological 

 Survey, fully confirmed the correctness of the microscopical 

 determination. The material analyzed was derived from a 

 biotite porphyrite of the Ten Mile District, Colorado, in which 

 the mineral occurred in exceptional abundance. The pro- 

 cess of separation and analysis is described by Dr. Hillebrand 

 as follows : " The mineral supposed to be allanite was separa- 

 ted from the rock, together with much magnetite and some 

 zircon, by means of the Sonstadt solution. The magnetite being 

 removed by a magnet, the other minerals were left quite free 

 from further admixture. They formed approximately 0*05 

 per cent of the whole rock. 



" In order to preserve the zircon crystals intact, the mixture 

 was treated, without pulverization, for many days in a platinum 

 crucible with hydrochloric acid. The residue was zircon and 

 silica retaining the original form of the allanite fragments. 

 This silica after filtration was entirely soluble in hot sodium 

 carbonate. After separating silica in the hydrochloric acid 

 solution, the latter was boiled with potassium hydrate. The 

 filtrate then showed much alumina and lime, and very little 

 magnesia. The precipitate by potassium hydrate was dissolved 

 in hydrochloric acid, diluted, and to it a concentrated solution 

 of oxalic acid added. The precipitate, at first curdy, was igni- 

 ted, dissolved in sulphuric acid, evaporated, and ignited gently, 

 the sulphates dissolved in cold water, and crystals of potassium 

 sulphate added. After washing the insoluble double sulphate 

 formed with a potassium sulphate solution, ammonia formed no 

 precipitate in the filtrate, showing the absence of erbium and 

 yttrium. The double sulphates dissolved very readily in 

 water acidulated with hydrochloric acid, and were then decom- 

 posed by oxalic acid ; the ignited precipitate was brown, readily 

 soluble in hydrochloric acid with evolution of chlorine, indica- 

 ting thereby the presence of both cerium and lanthanum, and 

 absence of thorium. No didymium absorption lines were 

 visible in the spectroscope. The oxalates, when dissolved in 

 strong nitric acid and boiled with lead dioxide, gave a yellow 

 solution showing the presence of cerium. Further tests were 

 rendered impossible by the loss of the material. 



" Although in the beginning only a qualitative analysis was 

 contemplated, owing to the small amount of material, neverthe- 

 less the silica, alumina, ferric oxide, mixed cerium and lantha- 

 num oxides, and the lime were weighed, and found to bear to 

 one another the avarage ratio of those constituents in allanite." 



Considering the identity of the mineral as established, the 



