the average being £60, which is the price usually adopted.
Sulphate of Lime and Alkaline Salts (consisting chiefly of soda) are generally estimated at £l per ton; and potash in those cases, in which it is necessary to take it into account, is usually valued at from £20 to £30 per ton, the former being its value in kelp, the form in which it can be most cheaply purchased.
Nitrate of Soda is usually sold at from £15 to £15: 10s. per ton, and, making allowance for impurities, £16 may be taken as the value of the pure salt.
Biphosphate of Lime, Soluble Phosphates.—Considerable difficulty is experienced in estimating the value of these substances, because they are not met with in commerce alone, or in any form except that of superphosphate, and the prices at which they are sold in different samples of that manure differ excessively. The only course by which any result can be obtained, is to determine the average price of a good superphosphate, and putting the values already ascertained on all the other constituents to reckon the difference between that sum and the market price as the value of soluble phosphates. Throwing out, as inferior, all samples containing less than 10 per cent of soluble phosphates, and taking the good only, I find that the average composition of the phosphates in the market during the present year has been—
| Water | 10·71 |
| Organic matter | 9·33 |
| Biphosphate of lime equivalent to 19·43 "soluble phosphates" | 12·45 |
| Insoluble phosphates | 14·78 |
| Sulphate of lime | 45·24 |
| Alkaline salts | 2·11 |
| Sand | 5·38 |
| ——— | |
| 100·00 | |
| Ammonia | 1·71 |
It is more difficult to fix the average price of superphosphate, as in many cases no information could be obtained on this point; but among those analyzed were samples at all prices, from £7 up to £10: 10s. per ton, so that on the whole, £8 may be assumed as an average, and in that case soluble phosphates are worth £27: 19s. per ton. Had the inferior samples been included, the price would have been higher, and in fact the rate at which soluble phosphates have been commonly estimated is £30 per ton, or £46: 16s. for biphosphate of lime, although sometimes the former have been reckoned as low as £25, with a corresponding rate for the latter. It is important that biphosphate of lime and soluble phosphates should not be confounded with one another in valuing a manure, the latter having one and a half times the value of the former.
As manures are liable to considerable fluctuations in price, the value attached to each of their constituents ought to be varied with the state of the market; but it is obviously impossible for the farmer to watch the changes in price with such minuteness as to enable him to do this, and it is much more convenient, as well as safer, to adopt a fixed average, which can be used with reasonable accuracy at all times. The fact is, that this system of valuation is only an approximation to the truth; and if absolute accuracy were aimed at, it would be necessary to vary the estimates, not only at different times, but at different localities at the same time, and to some extent also according to the kind of manure. The price of soluble phosphates more especially, fluctuates to a great extent, being practically fixed by each manufacturer according to the facilities which his position or command of raw material offer for producing them at a low rate. We thus find that when made from bones alone, the cost of that substance is not unfrequently as high as £40 per ton, and when bone-ash alone is used it is sometimes as low as £20. Such extreme differences, of course, cannot be taken into account in the system of valuation adopted, where all that can be done is to take average values, which, when applied to average samples, ought to bring out their value.
The data which have already been given regarding the price of the individual constituents of manures can be applied to the determination of the value of any mixture in two different ways by means of the subjoined table:—
| Price per Ton. | Per cent per Ton. | |
| Ammonia | £60 0 0 | £0 12 0 |
| Insoluble phosphates | 7 0 0 | 0 1 5 |
| Do. in phosphatic guanos | 10 0 0 | 0 2 0 |
| Soluble phosphates | 30 0 0 | 0 6 0 |
| Biphosphate of lime | 46 16 0 | 0 9 4-1/2 |
| Alkaline salts | 1 0 0 | 0 0 2-4/10 |
| Sulphate of lime | 1 0 0 | 0 0 2-4/10 |
| Potash | 20 0 0 | 0 4 0 |
| Nitrate of soda | 16 0 0 | 0 3 2-1/2 |
| Organic matter | 0 10 0 | 0 0 1-1/4 |
Supposing it be desired to calculate the value of a manure by the first column, it is obvious that if we suppose 100 tons to be purchased, the per centages of the different constituents shewn in the analysis will give the number of tons of each contained in 100 tons of the mixture, and, selecting the analysis of the superphosphate given in a previous page, we proceed in the calculation as follows:—