PLANT AND ANIMAL REFUSE AS MANURE 75 



can then be ground up in a mill very much more finely than 

 they could without preliminary treatment for the removal 

 of fat. The manufacture of these materials into bone 

 manures is described further on p. 173. 



Wool Wastes. Yorkshire mills produce a large amount 

 of waste material which is known as " shoddy." Old woollen 

 materials can be torn up in machines to produce fibre for 

 re-making into cloth. During this process a large quantity 

 of the wool becomes so cut up that it is unfit for spinning. 

 There are also similar wastes from carpet, silk and other 

 factories. Wool contains nitrogenous organic compounds 

 which decompose in the soil with the ultimate production of 

 nitrate, but cotton, having no nitrogen, produces no such 

 result. Pure wool shoddy may contain as much as 15 % of 

 nitrogen, and is much valued by the hop growers of Kent. 

 By treating with sulphuric acid, wool can also be used as a 

 valuable ingredient in admixture with other materials for 

 fertilizing purposes. Shoddy is rather a slow-acting manure, 

 but has given very beneficial results on many crops. Some of 

 its value is due to its physical properties, such as its high 

 capacity for absorbing water. It is usually ploughed in 

 during the winter at the rate of 1-2 tons per acre. 



Potash is an important by-product of the wool-combing 

 industry. The method of washing raw wool that is 

 usually adopted is to place it in hot water with alkali in very 

 weak solution. By these means the fatty matter can be 

 easily removed, but the liquors are more difficult to deal 

 with. An important improvement consists in first washing 

 the wool in cold water so that a small quantity of potassium 

 carbonate is obtained in solution relatively free from fat. 

 This practice was at one time very common because, owing 

 to the high cost of soda, the potassium carbonate so obtained 

 could be utilized for many purposes. The method has been 

 revived recently owing to the shortage of potash. When 

 the wool is first washed with water the solution is best 

 evaporated to dryness and calcined, but the cost of evapora- 

 tion and calcining is very considerable. 



In the " Cardem " process the centrifugal wool- scouring 



