USE OF THE PRECEDING TABLE. 301 



find that the relation between the weight of potatoes as they come 

 from the ground, and that of the tops or haum, supposed to be dry, 

 is as 100 is to 6.4. 



The tubers contain : 

 Azote 0.0036 per 10000 parts ; and 220 lbs. contain 0.729 of a lb. of 



azote, and are worth Is. 8d. 



The tops or haum, dry, contain : 

 Azote 0.0230 per 10000 parts ; and 14 lbs. contain 0.330 of a pound 



of azote. 

 Total of azote 1.122. 

 Now 20.4 lbs. of cake which would be required to produce 220 



lbs. of potatoes, contain 1.1 lb. of azote, and are worth 0«. lid. 



Difference ..Is. Oid.. 



The oil-cake at the price of 3*. 2d. per cwt. may therefore be ad- 

 vantageously used for the production of potatoes : rent, labor, seed, 

 &c., considered as before. At the price of 7s. 6d. or 8^. 6d. per 

 cwt., however, to which oil-cake occasionally rises, it would not be 

 possible to employ it profitably in this way. The cost of the manure 

 would then amount to nearly as much as the value of the crop. 



The equivalent numbers in the table express the relative values 

 of different manures ; they proclaim the proportions in which one 

 substance must be substituted for another, and when purchases are 

 to be made, they will show at a glance which is the article that is 

 really, and in fact, the cheapest. The equivalent number of one 

 variety of oil-cake, for instance, is 7.25 ; that of farm-yard dung is 

 100 ; which is as much as to say that in reference to mere fertilizing 

 elements, 100 parts — lbs. cwts. or tons, of farm-yard dung may be 

 replaced by 7^ parts — lbs. cwts. or tons of oil-cake ; — 2 cwt. of 

 farm-dung, for instance, by 14|^ lbs. of cake. The 2 cwt. of farm- 

 dung is valued in the table at 6d., or about 5s. per ton ; the 14| lbs. 

 of cake would cost 5^d. It is obvious, therefore, that even at the 

 above low price of oil-cake, there would be no real advantage in 

 substituting it generally for farm-yard dung ; in situations, however, 

 remote from large towns, where it is almost impossible to procure 

 dung, or where the carriage of large masses of dung would be both 

 difficult and expensive, there would then be advantage in the sub- 

 stitution. 



Woollen rags at the price of about 2*. 10c?. per cwt. are more pro- 

 fitable than farm-yard dung at 3^. per cwt. The equivalent of the 

 rags is 2.22, and this quantity (2.22 lbs. avoird.) of rags is worth 

 about ^d. ; by the substitution of the rags for farm-yard manure, 

 therefore, a saving is effected of about 2|<i. on every cwt. of the 

 latter that must have been employed. In good farming, however, 

 it is less with reference to the money advantage of substituting one 

 manure for another, that calculations are made, than with reference 

 to the possibility of procuring either one manure or another at a 

 moderate price. The estimated value of the dung in one of the 

 columns of the table gives us at once the price that may be paid for 

 it ; for this purpose it is enough to know the value of standard dung : 

 let this be as it usually is, 3^. per cwt. ; if we would now know 

 what maj be paid for a hundred weight of bones simply ('ried in th« 



26 



