190 Chemical Examination of Algerite. 
«The only modifications of the primary, which have been 
observed, are the replacement of the oblique and lateral edges 
of the prism by single planes; they exhibit no strize." 
The crystals are very sparsely disseminated through the 
coarsely crystalline limestone, and it was with difficulty, that 
I could obtain 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 inter- 
penetrated by the matrix, which is a pure calcareous spar. - 
The specific gravity of four light-colored translucent crys- 
tals which had been selected with great care and weighed 
‘2685 grammes, was found to be 2:697, while 1:8 grammes 
of fragments gave the number 2-712 ; and some coarser crys- 
tals were found to have a specific gravity of 2-948. ‘The 
hardness when unaffected 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. Pulver- 
ized 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 erystals selected for analysis were hard, semi-translu- 
cent, and undecomposed ; 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 cale 
spar; by digestion it takes up a portion of potash, alumina, 
iron, and magnesia, while a white granular residue remains. 
It is however impossible in this way to effect a complete 
analysis of the mineral, for even after long digestion the de- 
composition is found to be very incomplete. It was accord- 
ingly 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 oiai while the Jime is- evidently present 
