76 FERTILISERS CONTAINING NITROGEN [chap. ii. 



cent, of phosphoric acid, while species of Laminaria 

 from the same locality contained from 0-15 to 0-5 of 

 nitrogen, and 0-2 to 0-3 of phosphoric acid. 



It is needless to continue the enumeration of the 

 substances which from time to time are employed as 

 manures : leather in the form of dust, turnings and 

 shavings of horn, meat and cheese that have been 

 condemned for food, all find their way from time to 

 time either to the manure manufacturer or to the land. 



The only general rule one can apply to such 

 residues is to buy them on their approximate nitrogen 

 content, paying a low unit price because of their slow- 

 ness of action, and also to take into account the 

 comparative fineness of division and ease of spreading. 

 Even the most resistant material, such as leather or 

 horn, will decay if it is only freely enough divided and 

 disseminated through the soil 



