This gathering of useless nitrogen from the air, and making it over into plant-food cannot go on in a soil destitute of organic matter, requires in fact that vegetable remains or humified substances of some sort be present there. The evidence of this statement, whose truth was maintained years ago as a matter of opinion by many of the older chemists, has recently become nearly a matter of demonstration by the investigations of Boussingault and Knop, while the explanation of it is furnished by the researches of Schœnbein and Zabelin. To attempt any elucidation of it here would require more space than is at our disposal.
It is plain from the contents of this paragraph that peat or swamp muck is, in general, an abundant source of nitrogen, and is often therefore an extremely cheap means of replacing the most rare and costly fertilizers.
II.—With regard to the inorganic matters of peat considered as food to plants, it is obvious, that, leaving out of the account for the present, some exceptional cases, they are useful as far as they go.
In the ashes of peats, we almost always find small quantities of sulphate of lime, magnesia and phosphoric acid. Potash and soda too, are often present, though rarely to any considerable amount. Carbonate and sulphate of lime are large ingredients of the ashes of about one-half, of the thirty-three peats and swamp mucks I have examined. The ashes of the other half are largely mixed with sand and soil, but in most cases also contain considerable sulphate of lime, and often carbonates of lime and magnesia.
In one swamp-muck, from Milford, Conn., there was found but two per cent. of ash, at least one-half of which was sand, and the remainder sulphate of lime, (gypsum.) In other samples 20, 30, 50 and even 60 per cent. remained after burning off the organic matter. In these cases the ash is chiefly sand. The amount of ash found in those peats which were most free from sand, ranges from five to nine per cent. Probably the average proportion of true ash, viz.: that derived from the organic matters themselves, not including sand and accidental ingredients, is not far from five per cent.
In twenty-two specimens of European peat, examined by Websky, Jæckel, Walz, Wiegmann, Einhof and Berthier, eleven contained from 0.6 to 3.5 per cent. of ash. The other eleven yielded from 5.3 to 22 per cent. The average of the former was 2.4, that of the latter 12.7 per cent. Most of these contained a considerable proportion of sand or soil.
Variation in the composition as well as in the quantity of ash is very great.
Three analyses of peat-ashes have been executed at the author's instance with the subjoined results:
ANALYSIS OF PEAT-ASHES.
| A. | B. | C. | |
| Potash | 0.69 | 0.80 | 3.46 |
| Soda | 0.58 | - | trace. |
| Lime | 40.52 | 35.59 | 6.60 |
| Magnesia | 6.06 | 4.92 | 1.05 |
| Oxide of iron and alumina | 5.17 | 9.08 | 15.59 |
| Phosphoric acid | 0.50 | 0.77 | 1.55 |
| Sulphuric acid | 5.52 | 10.41 | 4.04 |
| Chlorine | 0.15 | 0.43 | 0.70 |
| Soluble silica | 8.23 | 1.40 } | |
| Carbonic acid | 19.60 | 22.28 } | 67.01 |
| Sand | 12.11 | 15.04 } | |
| 99.13 | 100.74 | 100.00 |