Certain fertilizers have the faculty of modifying surface tension and thus change the power of the soil in its attraction for moisture. In this way such fertilizers act favorably on plant growth, both by providing plant food and by supplying needed moisture. =168. Surface Tension of Fertilizers.=—Whitney gives the following data in respect of the surface tension of aqueous solutions of some of the more common fertilizing materials. It is expressed in gram meters per square meter, _i. e._, on a square meter of liquid surface there is sufficient energy to lift the given number of grams to the height of one meter. SURFACE TENSION OF VARIOUS FERTILIZING SOLUTIONS. Solution of— Specific gravity. Gram meters per square meter. Salt 1.070 7.975 Kainite 1.053 7.900 Lime 1.002 7.696 Water 1.000 7.668 Acid phosphate 1.005 7.656 Plaster 1.000 7.638 Ammonia 0.960 6.869 Urine 1.026 6.615 Magnesium chlorid 1.1000 7.964 Basic slag 1.0012 7.890 Marl 1.0013 7.855 Potassium chlorid 1.1000 7.853 Ammonium sulfate 1.1000 7.834 Dried blood 1.0001 7.764 Ground bone 1.0007 7.749 Sodium nitrate 1.1000 7.730 Sodium sulfate 1.1000 7.730 Wood ashes 1.0038 7.674 Potassium nitrate 1.1000 7.661 Potassium sulfate 1.0830 7.658 Ammonium nitrate 1.1000 7.656 Dried fish 1.0026 7.594 Stable manure 1.0013 7.464 Cotton-seed meal 1.0054 6.534 Tankage 1.0169 4.844 Cotton seed 1.0070 4.788 SURFACE TENSION OF SOIL EXTRACTS. Kind of Soil. Specific gravity. Surface tension. Kentucky blue grass 1.000 7.244 Triassic red sandstone 1.000 7.244 Wheat soil 1.000 7.098 Garden soil 1.000 7.089