LOSS OF SIUCA AND FL,UORIN 22/ 



197. Treatment of the Solution. The flask containing the 

 nitrate is filled to the mark with cold water, and the solution 

 is thoroughly mixed by twice pouring into a dry beaker and 

 returning to the flask. Cold water is used for washing the res- 

 idue, since if hot water be used, the sesquichlorids are apt to 

 become basic and insoluble, and hence to remain in the residue 

 and on the filter paper. Besides, as the flask is to be filled to the 

 mark, the contents must be cold before any volumetric measure- 

 ments can be made. The solution may then be used for the 

 general determination of the dissolved matters therein. 



198. Silica and Insoluble Bodies. Wyatt describes the follow- 

 ing method for determining the total insoluble or siliceous matters 

 in a mineral phosphate. 85 Five grams of the fine sample are 

 placed in a porcelain dish with about 30 cubic centimeters of 

 aqua regia. The dish is covered with a funnel, placed on a sand 

 bath, and, after solution is complete, evaporated to dryness with 

 care to prevent spluttering. When dry, the residue is moistened 

 with hydrochloric acid and again dried, rubbing meanwhile to a 

 fine powder. The heat of the bath is then increased to 125 

 and maintained at this temperature for about 10 minutes. When 

 cool, the residue is treated with 50 cubic centimeters of hydro- 

 chloric acid for 15 minutes. The acid is then diluted and fil- 

 tered on a gooch, which is washed with hot water until the filtrate 

 amounts to a quarter of a liter. The residue in the crucible 

 is dried, ignited and weighed. Unless the solution be subse- 

 quently boiled with nitric acid, all the phosphoric acid may not 

 be retained in the ortho form. 



199. Loss of Silica and Fluorin. It is difficult to estimate 

 the total silica by the ordinary methods of mineral analysis. This 

 is due to the fact that in an acid solution of a substance con- 

 taining silicates and fluorids the whole of the silica or the fluorin, 

 as the case may be, may escape as silicofluorid on evaporation. 

 Again, it is not easy to decompose calcium phosphate by fusing 

 with sodium carbonate. If an attempt be made to do this, how- 

 ever, the process should be conducted as follows : A portion of 

 the sample is ground to an impalpable powder in an agate mor- 

 tar. From one to two grams of the substance are mixed with 



85 Phosphates of America, 4th Edition, 1892 : 147. 



