341 Mr. D. Forbes on Evansitc, a new Mineral Species. 



24*877 grs., translucent and colourless, heated in a water- 

 bath at ."212° Fahr, for twenty hours, left 20*25 grs. residue, being 

 4*627 grs. water, or equal to 13*69 per cent, water given off at 

 212° Fahr. ; on further heating to redness left 14*94 grs. residue, 

 thus giving a total of 5*31 grs. water, or equivalent to 39*91 

 per cent. 



The average of these four experiments affords 39*945 per cent, 

 water. 



Determination of the Insoluble Matter (Silica). 



18*07 grs. of the mineral were dissolved in hydrochloric 

 acid with addition of a little nitric acid ; some flakes remained 

 persistently insoluble, and were collected on a filter, washed, 

 dried and incinerated, and weighed 0*250 gr., or equal to 1'39 

 per cent. 



13*365 grs. of the translucent but yellow-coloured mineral, 

 after having been previously ignited to determine the amount of 

 water present, were now dissolved in nitrohydrochloric acid ; the 

 insoluble residue collected on a filter, washed, and determined after 

 incineration, weighed 0*46 gr., or equivalent to 3*44 per cent. 

 I satisfied myself, however, that this result is quite erroneous 

 and much too high, owing to a part of the phosphate of alumina 

 in the mineral becoming itself insoluble, through the previous 

 heating it had been submitted to in determining the percentage 

 of water in it. 



Determination of the Phosphoric Acid. 



22*22 grs. of the white translucent mineral were dissolved 

 in nitrohydrochloric acid, and to the solution an excess of a so- 

 lution of molybdate of ammonia, previously rendered strongly 

 acid by addition of nitric acid in large excess, was added until 

 all phosphoric acid present was precipitated in the form of the 

 yellow phosphomolybdate of ammonia. After filtration this pre- 

 cipitate was dissolved in ammonia, and the solution then preci- 

 pitated by adding a mixed solution of sulphate of magnesia, 

 chloride of ammonium, and caustic ammonia. The precipitate 

 of phosphate of ammonia and magnesia was allowed to stand for 

 twelve hours, then filtered off, washed with ammonia-water, and 

 determined on ignition, affording 6*40 grs. pyrophosphate of 

 magnesia, equivalent to 4*09 grs. phosphoric acid, or 18*42 per 

 cent, phosphoric acid in the mineral. 



Another estimation of the phosphoric acid in the mineral was 

 made by Girard's modification of Reynoso's process, as follows : — 



15*38 grs. were dissolved in nitric acid, and 22 grs. of me- 

 tallic tin then added to the solution and boiled until entirely 

 oxidized ; the solution was then filtered off, and the insoluble 

 oxide and phosphate of tin dissolved in excess of sulphide of 

 ammonium by digestion ; the solution was filtered from some 



