xiii.] VALUATION OF MANURES 267 



of doing this is by what is called the unit system, the 

 unit being i per cent, of a ton of the fertilising con- 

 stituents — nitrogen, phosphate of lime, and potash. The 

 value of a unit of each of these constituents will vary 

 with market fluctuations, and to a certain extent with 

 the place of delivery. Thus the exact values prevailing 

 at any moment can only be obtained by special calcula- 

 tions, but for purposes of comparing one fertiliser 

 against another in the United Kingdom it will be 

 sufficiently accurate to consider that the unit of nitrogen 

 is worth 14s., the unit of phosphate of lime 2s. if it is 

 soluble, and isd. if insoluble, while the unit of potash 

 may be reckoned as worth 4s. Working on these 

 principles, fish guano containing 7\ per cent of nitrogen 

 and 1 3 per cent of phosphate, should be worth about 

 12 IS., made up as follows : — 



£ 8. D. 



7^ of nitrogen at 14s. . • = 55° 



+ 13 of phosphate at IS. 3d. . = o 16 3 



Total. . . 613 



As this fertiliser was offered to a farmer at 146s., it must 

 be regarded as dear when compared with the meat meal 

 containing 7 per cent, of nitrogen and 30 per cent, of 

 phosphate, which was offered at the same time at 127s. 

 6d. Valued on the same principle, this later manure is 

 worth, 7 of nitrogen at 14s. = 98s. -f 30 of phosphate at 

 IS. 3d. = 37s. 6d., or a total of 13SS. 6d. By making 

 valuations in this fashion of the manures on offer in the 

 market, the farmer is often able to buy much more 

 cheaply than he would if he stuck to the same kind of 

 fertiliser year by year, independently of their fluctua- 

 tions in market value. For some kinds of fertilisers 

 which are subject to natural variations it is very 

 necessary that the farmer should obtain an analysis 

 after the delivery of the bulk, in order to compare it 



