_Insoluble Phosphates._--These are purchased alone, chiefly in the form of coprolites and bone-ash, or the spent animal charcoal of the sugar refiners. Ground coprolites, containing about 58 per cent of phosphates, sell at L2: 12s. per ton, which is at the rate of L4: 8s. for pure phosphates. Bone-ash varies considerably in price, but of late samples containing 70 per cent of phosphates have sold as low as L4: 10s. per ton, and consequently pure phosphates in this form are worth L6: 8s. per ton. Although these are the only forms in which phosphates are purchased alone, it is possible to determine the price at which they are sold in bones and phosphatic guanos, by first deducting the value of the ammonia they contain, and assuming the remainder to represent the price paid for the phosphates. In this way we find the following values for insoluble phosphates:-- In Coprolites L4 10 0 Bone-ash 6 8 0 Bones 7 5 0 Phosphatic guanos 10 0 0 It is to be observed that these are actual prices, and they are liable to fluctuate with the state of the market, although they are pretty fair averages. It is important to notice how much they vary in the different forms; the farmer who buys a phosphatic guano paying for phosphates a much higher price than he could have obtained those for in other substances--a difference which must be attributed to the high state of division in which they exist in the guano. We do not here enter upon the question how far this difference in price is justified; we are content with the fact that it exists, and we are compelled to estimate the value of phosphates in a phosphatic guano at the price given above, although in Peruvian guano they are sold at a lower rate. For all other manures, of which bones and bone-ash form the basis, L7 may be taken as a fair price, and it is that usually adopted, though L8 and L10 have sometimes been assumed as the average. _Ammonia_ is met with in commerce as muriate and sulphate of ammonia. The former, owing to its high price, is practically excluded from use as a manure; the latter sells at present at from L15 to L15: 10s. per ton, and, making allowance for the usual amount of impurity (5 or 6 per cent), the actual ammonia is worth about L63 per ton. Calculating from other substances it appears that ammonia is worth, per ton, in-- Sulphate of ammonia L63 0 0 Bones 61 0 0 Peruvian guano 57 0 0 the average being L60, which is the price usually adopted. _Sulphate of Lime_ and _Alkaline Salts_ (consisting chiefly of soda) are generally estimated at Ll per ton; and potash in those cases, in which it is necessary to take it into account, is usually valued at from L20 to L30 per ton, the former being its value in kelp, the form in which it can be most cheaply purchased.