CHAPTER VI.--POSITION OF POTASH IN AGRICULTURE. Potash of less importance than phosphoric acid 212 Occurrence of potash 213 Felspar and other potash minerals 213 Stassfurt salts 214 Occurrence of saltpetre 215 Occurrence of potash in the soil 215 Potash chiefly in insoluble condition in soils 216 Percentage of potash in plants and plant-ash 216 Occurrence of potash in animal tissue 217 Sources of loss of potash 217 Amount of potash removed in crops 218 Amount of potash removed in milk 218 Potash manures 218 APPENDIX TO CHAPTER VI. NOTE I. Amount of potash in different minerals 220 II. Quantity of potash obtained from 1000 lb. of different kinds of vegetation in the manufacture of potashes 220 PART III.--MANURES. CHAPTER VII.--FARMYARD MANURE. Variation in its composition 223 Made up of three classes of constituents 224 _Solid excreta_-- Its nature 224 Difference in composition of the solid excreta of the different farm animals 224 Causes of this difference 225 Percentage of manurial ingredients in solid excreta of different animals 226 _Urine_-- Its nature 228 Variation in its composition 229 Causes of this variation 229 Manurial value of the urine of the different farm animals 230 Percentage of the _organic matter_, _nitrogen_, and _mineral substances_ in the food, voided in the solid excreta and urine 232 Comparison of manurial value of total excrements of the different farm animals 234 Nature of changes undergone by food in process of digestion 235 _Litter_-- Its uses 236