=224. Introduction.=—The potash present in unfertilized soils has been derived from the decay of rocks containing potash minerals. Among these potash producers feldspars are perhaps the most important. For a discussion of the nature of their decomposition and the causes producing it the first part of volume first may be consulted. Potash is quite as extensively distributed as phosphoric acid and no true soils are without it in some proportion. Its presence is necessary to plant growth and it forms, in combination with organic and mineral acids, an essential part of the vegetable organism, existing in exceptionally rich quantities in the seeds. It is possible that potash salts, such as the chlorid, sulfate, and phosphate may be assimilated as such, but, as with other compounds, we must not deny to the plant the remarkable faculty of being able to decompose its most stable salts and to form from the fragments thus produced entirely new compounds. This is certainly true of the potash compounds existing in plants in combination with organic acids. The potash which is assimilated by plants exists in the soil chiefly in a mineral state, and that added as fertilizer is chiefly in the same condition. That part of the potash in a soil arising directly from the decomposition of vegetable matters may exist partly in organic combination, but this portion, in comparison with the total quantity absorbed by the plant, is insignificant. It is then safe to assume that at least a considerable part of the potash absorbed by the plant is decomposed from its original form of combination by the vegetable biochemical forces, and is finally incorporated in the plant tissues in forms determined by the same powerful forces of vegetable metabolism. The analyst is not often called upon to investigate the forms in which the potash exists in plants, when engaged in investigation of fertilizers. It is chiefly found in combination with organic and phosphoric acids, and on ignition will appear as phosphate or carbonate in the ash. =225. Forms in which Potash is Found in Fertilizers.=—The chief natural sources of potash used in fertilizer fabrication are: First, organic compounds, such as desiccated mineral matters, tobacco waste, cottonseed hulls, etc.; second, the ash derived from burning terrestrial plants of all kinds; third, the natural mineral deposits, such as Stassfurt salts.