314 Penfield — Chejnical Composition of Hamlinite. 



development and rounding, the prismatic faces have a tendency 

 toward a steep rhombohedron, and the basal planes are marked 

 by triangular prominences. 



The crystals attain at times a diameter of 3 to 4 mm , but are 

 not well adapted for measurement owing to the vicinal char- 

 acter of the faces. The following measurements can claim to 

 be only approximations, since there were usually several reflec- 

 tions of the signal of the goniometer from each face, and it was 

 impossible to tell upon which one the cross-hair of the tele- 

 scope should be placed. The calculated angles are those 

 derived from measurements of the hamlinite from Stoneham, 

 c= 1*135, but the crystals from that locality showed a vicinal 

 development of their faces, and the values can not, therefore, 

 be considered as very exact. 



Measured. Calculated. 



r^r, 1011^1101= 88° 41' 87° 2' 



f^f 0221/^2021 = 109 11 108 2 



r A /, 1011^0221= 54 44 and 54° 47' 54 1 



It was found to be practically impossible to select by hand- 

 picking a sufficient quantity of the pure hamlinite crystals for 

 an analysis, and, therefore, a number of specimens upon which 

 the crystals were observed were pulverized, and the hamlinite 

 separated from the other minerals by means of the heavy 

 liquids. Apatite, however, could not be thus separated, but, 

 owing to the fact that hamlinite is almost insoluble in boiling 

 dilute hydrochloric acid, it was possible by treatment with 

 successive portions of acid until the solution gave no test for 

 calcium to remove the apatite completely. All possible pre- 

 cautions were taken to make the separation and purification of 

 the mineral as complete as possible, and the mineral, when 

 examined with the microscope, showed no visible impurity. 

 The specific gravity of the hamlinite varied considerably, that 

 portion which was taken for the chemical analysis being 

 between 3*159 and 3*283, while some of the mineral was still a 

 trifle higher and some a little lower. 



A qualitative analysis indicated the presence of aluminium, 

 strontium, barium, phosphorus, fluorine and water, and the 

 absence of calcium and beryllium. In the quantitative analyses 

 the strontium and barium were weighed together as sulphates 

 and subsequently separated as recommended by Fresenius,* by 

 a double precipitation of the barium as chromate. The fluorine 

 was weighed as calcium fluoride, and the latter was tested and 

 found to be pure by conversion into sulphate. Water was 

 determined in two ways ; first by fusing with dry sodium car- 

 bonate and weighing the water directly, f second by loss on 



* Zeitsch. fur anal. Chemie, xxix, p. 413, 1890. 

 f This Journal, xlviii, p. 87, 1894. 



