EXPERIMENT STATION BULLETINS. 295 



20 per cent moisture content the freezing point depression of the quartz was 

 0.028°, ferrugineous sandstone 0.145°, apophylUte 0.175°, shale 0.119, apatite 

 0.059, etc., while at 75 per cent moisture, the depression was 0.008°, 0.057°, 

 0.069°, 0.050°, and 0.022° respectively. In such materials as calcite, hem- 

 atite, marble, limonite, etc., the depression at the low moisture content was 

 practically the same as at the high. 



If we apply the formula which was established in a mixture of all the min- 

 erals and rocks employed that a depression of 0.002°C is equivalent to 100 

 parts per million of solution then the concentration of the solution of the 

 rocks and minerals varies from 100 p.p.m. in quartz, to 711 in ferrugineous 

 sandstone, to 975 in apophyllite at 75 per cent of moisture content, and 350, 

 1,811 and 2,187 p.p.m. respectively at 20 per cent of moisture. 



It is readily realized, of course, that the solutions of the different rocks 

 and minerals may contain soluble material of different degrees of dissociation 

 which may affect the freezing point depression slightly differently. The 

 above formula, therefore, which was obtained from an average of all the 

 rocks and minerals emploj^d may not be correctly applied to all the different 

 rocks and minerals. It is believed, however, that it gives a very close ap- 

 proximation of the concentration of the solution of these various materials, 

 in parts per million. 



The above appreciable amount of readily soluble material in the powder 

 of the different rocks and minerals is obtained, with few exceptions, only 

 with the unleached powder. When the powder is leached with distilled 

 water, the readily soluble material is washed away and very little new ma- 

 terial goes into solution to take its place, as indicated by the much smaller 

 freezing point depression. This point is well exemphfied by the data in 

 table 2. 



TABLE 2 



Amount of Soluble Material in Leached and Unleached Powder of Rocks 

 and Minerals. Figures Represent Freezing Point Depression. 



Unleached Leached 

 Name of Rocks and Minerals 75 per cent 75 per cent 



moisture moisture 



C° C° 



Banded biotite gneiss 0.015 .006 



Banded granite 021 .011 



Biotite granite 018 .010 



Biotite granite 020 .008 



Biotite granite 019 .010 



Compact lithographic limestone 018 .006 



Crumfjled mica-schist 010 .006 



Diabase..... 020 .008 



Diorite 020 .010 



Ferrugineous sandstone 050 .010 



Ferrugineous sandstone 057 .010 



Ferrugineous sandstone 010 .009 



Ferrugineous sandstone 010 .008 



Hornblend granite 020 .010 



Hornblend basalt 020 .007 



Hornblend gabbro 018 .009 



Hydrolic limestone 030 .015 



Marble (dolomitic) 013 .005 



