58 CHEMISTRY, GEOLOGY 



Woollen rags, cut into small pieces and mixed 

 with earth, make a very useful compost; and 

 they are much more effective if first decomposed 

 by sulphuric acid. 



The contents of privies, and the dung of horses, 

 cows, sheep, pigs, and birds, are all employed as 

 manures. Night-soil, now manufactured into an 

 article called poudrette, and birds' dung (guano), 

 are the most valuable as fertilizers : next, pigs' 

 dung, and lastly that of cows. 



Night-soil is most valuable as a manure, be- 

 cause men live upon a mixed animal and vege- 

 table diet, whereby their excrement is richer in 

 those substances which plants take up from the 

 soil. The dung of horses is more valuable than 

 that of cows, because the horse makes compar- 

 atively little water. Pigs' dung is by some 

 thought objectionable, as it has been supposed 

 to give a disagreeable taste and smell to crops 

 raised from it; an opinion, we think, without 



Questions. How are woollen rags best used a manure ? 

 Name some other sources of manures. What is manufac- 

 tured night-soil called ? What is guano ? Why is night- 

 soil most valuable as a manure ? Why is horse dung a better 

 fertilizer than that of cows? Why has pig dung been 

 deemed objectionable ? 



