536 
Value of Artificial Manures. 
manure, yet their distinctive character for one and the other crop 
remains and influences the nature of a compound manure accord- 
ingly. It is true that manure, when once placed in the soil, may 
be supposed to remain there for a future crop, but we cannot say 
that it will then be in the same available condition for plants ; 
and the true policy would undoubtedly be to add to any crop 
only that manure which it can at once appropriate. Perhaps of 
all other sources of difficulty in the estimation of the value of a 
manure this is the greatest — inasmuch as from the very nature 
of the substances employed in making manure a more or less 
mixed product is most commonly obtained. 
4. " The mechanical condition of a manure materially affects 
its value." The state of dryness, the size of the particles, the 
more or less perfect mixture of the various materials, all have an 
influence on the action of a manure which is not and cannot be 
taken account of in the statement of its composition ; so that a 
superior value in regard to the proportion of the ingredients 
may be more than neutralized by their faulty pulverization or 
admixture, leading to inequality of distribution and irregularity of 
the cro}) produced. 
5. " The commercial value of the same substance varies with 
the source," &c. Ammonia, in sulphate of ammonia, costs at the 
present price of that salt (15/.) about l\cl. per lb., whilst in 
Peruvian guano, at its present high price of 11/.,* the ammonia 
costs about 4fc?. per lb. In valuing a manure, which of these 
two data are we to employ ? The reason for the higher price of 
ammonia in sulphate is evidently that this salt has uses other 
than agricultural, which regulate its price, whilst guano has only 
one issue for consumption."!" 
6. " The price of the same substance in the same form 
varies continually from a variety of causes." It is obvious that 
as the supply of manure barely keeps pace with the requirements 
of agriculture, a variation of the prices of the ingredients of 
manure may be expected to occur at particular seasons. Accord- 
ingly, in the autumn of the year sulphate of ammonia and other 
such substances, chiefly used as top-dressings in the spring, will 
be cheaper than at other periods. Nitrate of soda, which is now 
largely used as a manure, fluctuates in price not only with the 
manure-market, but with a rise or fall in value of nitrate of 
potash. J Sulphate of potash to a great extent takes its price 
from that of alum, of which it is an ingredient. 
* The price of guano, as above quoted, -was given to me as that of the importers, 
on the 1st of the present month of November. 
t Very recently guano has come to be used in dyeing, some very beautiful 
specimens of silk, of which the colour was due to the employment of this sub- 
stance, being shown in the late French Exhibition. 
X Nitrute of potash, which, as is well known, is chiefly used in the manufacture 
