No. 105.1 



215 



have considered the composition of the graiuj nor to have remem- 

 bered the difference in the weight of the crop. Superficial reasoning 

 and general theories often appear beautiful ; but thorough investiga- 

 tion in detail, and the results of actual practice, will frequently ex- 

 hibit their uncertainty and error. 



A department of analysis, perhaps the least liable to erroneous 

 results, is the examination of manures. Fertilizing substances are 

 known by their effects applied separately to plants or in mixture ; 

 and by the fact that fertile soils and well grown plants are found to 

 contain them. Now, analysis will show what proportion of the ferti- 

 lizing materials exist in different kinds of manure ; and hence the 

 value of manures may be ascertained, at least to some extent, by a 

 previous chemical examination. A comparison of common manure 

 with guano, exhibits this principle in a striking light : 



A ton of manure yields 2 pounds and 4 ounces of potash. 



Here it will be seen that most of these enriching ingredients are 

 from thirty to seventy times as great in quantity in guano as in 

 common manure. Experiment accordingly proves that guano often 

 produces from thirty to seventy times as great a growth in plants, as 

 an equal quantity of manure. 



One of the most powerful manures is poudrette, a preparation from 

 night-soil. Let us see what kind of comparison analysis will draw 

 between this substance and guano : 



• London Ag. Gazette. 



