46 



PROCEEDINGS OF THE ACADEMY OF 



[1889. 



oo P : £~P = 44° 56' (over the pole.) 

 oo P : Poo = 60° 10' = 119° 50' 

 The angle of 115° 10' is uncertain within 5'. 

 One of the faces of P measured, was very small and 

 gave a dim reflection. All the other faces reflect 

 satisfactorily, even excellently. On one very small 

 crystal, the faces of a brachidome were observed, but 

 could not be measured. No cleavage has been observed 

 and therefore the longest dimension was chosen for 

 the main axis, in the position represented by the cut. 

 The parameters of the fundamental pyramid are : 

 a: b: c = 0. 73104: 1: 1.1640. 

 The optical properties could not be studied by rea- 

 son of the failure to obtain a thin section which 

 would transmit any light ; the color is so intense. 



The specific gravity was determined with 1.2475 

 grs. of pure crystals and found = 3. 582 B. B. 



When the powder is heated in closed tube it yields 

 much water without change of the ochre-yellow color. 

 Only at a red heat the color changes to a light brick- 

 red. In the oxydizing flame the mineral fuses to a 

 ,black scoria which is magnetic. On charcoal a light 

 volatile sublimate is produced and the garlic odor 

 of arsenic is developed. 



With borax only the reaction for iron is obtained. The mineral 

 dissolves easily in hot concentrated hydrochloric acid without effer- 

 vescence. The solution does not precipitate gold chloride (absent 

 Fe and As 2 3 .) 



In the course of the analysis, care was taken to obtain complete 

 precipitation of arsenic. Hydrogen sulphide was passed through 

 the solution three times, allowing the solution to stand 24 hours 



Only upon 



saturating 



the fourth time, no 



after each separation. 



precipitation resulted. As 2 S 3 -(- S was weighed ; a portion oxydized 

 and precipitated by Mg CI 2 . After filtering (N H 4 ), 2 was removed 

 by heat, H CI added and H 2 S passed through the solution. A 

 small quantity of Sb 2 S 3 was obtained. After igniting the ferric 

 hydrate, it was redissolved and by molybdic solution a slight yellow 

 precipitate produced. This proved to be due to phosphorus. 

 Water was determined in a separate portion. 

 0. 5520 of the substance gave. 

 0. 3430 As 2 S 3 + S. 



0. 3125 As 2 S 3 + S gave 0.2960 Mg 2 As 2 07. 

 0. 1685 Fe 2 O 3 . 

 0. 0820 Ca O 



0. 3050 substance lost by successive heating. 

 0. 0020 at 130° C. 

 . 0130 at 279° C. 



