[ tyrrell-graham] YUKONITE 17 



loosely held as water of hydration. The remaining water is only ex- 

 pelled after intense ignition at such a temperature that the mineral 

 suffers partial decomposition with disengagement of arsenious oxide; 

 this second portion of water may be regarded as being present as 

 water of constitution. 



The results of the complete analyses are given in columns 1 and 2 

 below: — 



1. 2. Calculated. 



CaO 10.00 10.14 9.74 



Fe-A 35.72 36.81 37.10 



AsjOg 34.06 33.83 33.33 . 



H2O 20.28 20.28 19.83 



100.06 101.06 100.00 



Water of hydration found 11.96% 



calculated 12.00% 



As might be expected by analogy with other amorphous substances, 

 the results ol^taincd from the analyses do not lead exactly to any very 

 simple formula for the mineral. The figures agree however in a general 

 way with those calculated for 2Ca3As208.3Fe2"As208.5Fe2'(OH)8. 

 23H2O and given above in column 3. The percentage of water (cor- 

 responding to 23H2O) which should be lost, at 100° C, by a mineral 

 having this composition is also in agreement with the loss actually 

 observed on heating the substance to this temperature. 



The substitution of 25H2O for 23H2O does not appreciably alter 

 the figures, and the composition of such a mineral might he expressed 

 by the general formula 



(Ca3,Fe'2")As208.Felf(OH)e.5H20, whore Ca,: Fe'}/ = 2:3. 



The mineral fuses readily, with intumescence, giving off white 

 fumes of arsenious oxide and leaving a black magnetic globule. In the 

 closed tube small fragments decrepitate violently and fly to pieces; 

 water is first given off and at a higher temperature white arsenious 

 oxide is deposited on the sides of the tube; when mixed with charcoal 

 a black arsenical mirror is obtained instead. 



The only well defined arsenates of iron and calcium at present 

 known are arseniosiderite , 2Ca3As208.Fe2*As^08.3Fe^(OH)Q and 

 mazapilite, Ca3As208.Fe2"As208.Fe"^2^2(C)H)2. Tire mineral desci'ibed 

 here can not be refei'red to either of these as regards its chemical 

 composition, and it is further quite distinct from them in its 

 physical characters. Neglecting the water of hydration, the com- 



