227. Cottonseed Hulls and Meal.—A considerable quantity of potash is added to the soil in cottonseed meal and hulls. The practice of burning the hulls cannot be recommended, although it is frequently practiced, for the incineration does not increase the quantities of phosphoric acid and potash, while it destroys the availability of the nitrogen. Nevertheless the analyst will often have to deal with samples of the raw materials above mentioned, as well as with the ash of the hulls, in which the potash can be determined by some one of the standard methods to be described. In general it is found that the hulls of seeds and the bark and leaves of plants have a greater percentage of ash than the interior portions. In the case of cottonseed however, an exception is to be noted. The cottonseed meal in the air-dried state has about seven per cent of ash, while the hulls have only about three. When it is remembered, however, that the greater part of the oil has been removed from the meal it will be seen that in the whole seed in the fresh state the discrepancy is not so marked.
In the crude ash of the hulls the percentage of potash varies generally from twenty to twenty-five per cent, but in numerous cases these limits are exceeded. In twelve samples of cottonseed hull ashes examined by the Connecticut station the mean percentage of potash in the crude sample was 22.47, and the extremes 15.57 and 30.24 per cent respectively.[188] In determining the value of the ash per ton the content of phosphoric acid must also be taken into account.
Cottonseed meal contains about 1.75 per cent of potash. Since the mean percentage of ash in the meal is seven, the mean content of potash in the crude ash is about twenty-five.
228. Wood Ashes.—Unleached wood ashes furnish an important quantity of potash fertilizer. The composition of the ash of woods is extremely variable. Not only do different varieties of trees have varying quantities of ash, but in the same variety the bark and twigs will give an ash quite different in quantity and composition from that furnished by the wood itself. In general the hard woods, such as hickory, oak, and maple, furnish a quality of ash superior for fertilizing purposes to that afforded by the soft woods, such as the pine and tulip trees.
The character of the unleached wood ashes found in the trade is indicated by the subjoined analyses. The first table contains the mean, maximum and minimum results of the analyses of ninety-seven samples by Goessmann.[189]
| Mean composition of wood ashes. | |||
|---|---|---|---|
| Means. | Maxima. | Minima. | |
| Potash | 5.5 | 10.2 | 2.5 |
| Phosphoric acid | 1.9 | 4.0 | 0.3 |
| Lime | 34.3 | 50.9 | 18.0 |
| Magnesia | 3.5 | 7.5 | 2.3 |
| Insoluble | 12.9 | 27.9 | 2.1 |
| Moisture | 12.0 | 28.6 | 0.7 |
| Carbon dioxid and undetermined | 29.9 | ||
In sixteen analyses made at the Connecticut station the data obtained are given below:[190]
| Means. | Maxima. | Minima. | |
|---|---|---|---|
| Potash | 5.3 | 7.7 | 4.0 |
| Phosphoric acid | 1.4 | 1.8 | 0.9 |
In fifteen analyses of ashes from domestic wood-fires in New England stoves, the following mean percentages of potash and phosphoric acid were found:
| Potash | 9.63 |
| Phosphoric acid | 2.32 |