Macadam[42] states that pigeon dung is the most concentrated. Hen manure contains the largest proportion of phosphates, and is followed by duck droppings. That of the goose is the least valuable. The preceding table is taken from his paper.
Procter[43] quotes the following, as a mean of 40 analyses of pigeon dung by Schulze:—
| Per cent. | |
| Water | 21·00 |
| Nitrogen | 2·53 |
| Phosphoric acid | 1·79 |
| Potash | 1·46 |
He remarks that the action of bird dung is more penetrating, but less softening and loosening than that of dog dung, and this effect may be explained by what has been said above.
Unfortunately, far less work has been done on the bird-dung bate than on the puer, and there is a wide field open for research in this direction.
CHAPTER III.
THE PHYSICS OF BATING.
“The most important aspect of any phenomenon, from a mathematical point of view, is that of a measurable quantity.” —Maxwell.