All of these forms of potash may be found in mixed fertilizers. While the final methods of analyses are the same in all cases the preliminary treatment is very different, being adapted to the nature of the sample. For analytical purposes, it is highly important that the potash be brought into a soluble mineral form, and that any organic matters which the sample contains be destroyed. If the sample be already of a mineral nature, it may still be mixed with other organic matter and then it requires treatment as above, for it is not safe always to rely solely on the solubility of the potash mineral, and the solution, moreover, in such cases, is likely to contain organic matter. In some States, only that portion of the potash soluble in water is allowed to be considered in official fertilizer work. In these cases it is evident that the organic matter present should not be destroyed in the original sample, but only in the aqueous solution. Since, however, the potash occluded in organic matter becomes constantly available as the process of decay goes on, it is not just to exclude it from the available supply. It may not be so immediately available as when in a soluble mineral state, but it is not long before it becomes valuable. Experience has shown, moreover, that phosphorus, nitrogen, and potash are all more valuable finally when applied to the soil in an organic form. This fact is a corroboration of the theory already advanced that all mineral compound bodies are probably decomposed before they enter as component parts into the tissues of the vegetable organism. It is highly probable, therefore, that the potash existing in organic compounds, finely divided and easily decomposed, is of equal, if not greater value to plant life than that already in a soluble mineral state. The organic matter, when present, is destroyed, either by ignition at a low temperature, or by moist combustion with an oxidizing agent before the potash is precipitated. ORGANIC SOURCES OF POTASH. =226. Tobacco Stems and Waste.=—Until within a few years tobacco stems and other waste from factories, were treated as a nuisance in this country, and burned or dumped into streams. By burning and saving the ash the potash contained in the stems and waste would be recovered in a form suitable for field use. The nitrogen, however, contained in these waste materials, both in the form of nicotin and of albuminoids would be lost. Ignition of this waste, therefore, should not be practiced. It should be prepared for use by grinding to a fine powder. Applied to the soil in this condition the powder may be useful as an insecticide as well as a fertilizer. Tobacco stems contain from twelve to twenty-seven per cent of moisture, and from twelve to twenty per cent of ash. The composition of the stems from two celebrated tobacco growing regions is subjoined:[185]