104 Chemical Examination of Algerite. 



may be obtained, parallel with the lateral planes of the prism, 

 sometimes possess considerable lustre ; they present a pearly re- 



flection in spots, the prevailing lustre being vitreous. In its gen- 



J 



eral aspect, when taken from near the surface, the mineral would 

 be described as without lustre and transparency. 



" The only modifications of the primary, which have been ob- 

 served, are the replacement of the oblique and lateral edges of 

 the prism by single planes; they exhibit no striae. 53 



The crystals are very sparsely disseminated through the coarsely 

 crystalline limestone, and it was with difficulty, that I could ob- 

 tain sufficient for the purposes of analysis. Those exposed to 

 the weather had become quite friable from partial decomposition 

 and the larger crystals were more or less interpenetrated by the 

 matrix which is a pure calcareous spar. 



The specific gravity of four light-colored translucent crystals 

 which had been selected with great care and weighed -2685 

 grammes, was found to be 2697, while 1-8 grammes of fragments 

 gave the number 2-712 ; and some coarser crystals were found 

 to have a specific gravity of 2*948. The hardness when unaf- 

 fected by exposure is 3-3-5 (Alger) ; it is brittle, easily separated 

 into fragments. Before the blowpipe it intumesces considerably, 

 and at a high temperature fuses with phosphorescence into a 

 white porous enamel. Pulverized and heated in a tube it gives 

 off abundance of water; the powder moistened with a solution 

 of nitrate of cobalt and heated on platinum foil, fuses into an 

 ultramarine-blue frit. 



The crystals selected for analysis were hard, semi-translucent 

 and undecom posed; their powder even when elutriated and 

 carefully dried was of a buff color which was not changed by 

 ignition. The action of hydrochloric acid upon it at first evolves 

 a little carbonic acid gas from the intermixed calc spar; by diges- 

 tion it takes up a portion of potash, alumina, iron and magnesia, 

 while a white granular residue remains. It is however impossi- 

 ble in this way to effect a complete analysis of the mineral, for 

 even after long digestion the decomposition is found to be very 

 incomplete. It was accordingly necessary to have recourse to 

 fusion with an alkaline carbonate ; the qualitative analysis thus 

 effected, showed the presence of silica, and alumina with small 

 quantities of iron, magnesia and lime ; the iron probably exists as 

 peroxyd from the color of the mineral, while the lime is evidently 

 present as a carbonate from the fact that it is at once taken up 

 by hydrochloric acid with effervescence. Another portion of the 

 mineral decomposed by hydrochloric acid, in Laurent's apparatus, 

 gave a large portion of potash, mixed with a little soda ; no lithia 

 could be detected in the alkalies. 



The quantitative analysis effected by the process above men- 

 tioned, gave the following results. 



