252 SOILS AND MANUEES 



some purposes it possesses certain advantages, and as it 

 is much cheaper, both per ton and per unit of nitrogen, 

 it has much to recommend it. The blood is collected in 

 slaughter-houses, and gently dried by steam heat, when 

 it is obtained in the form of dark brittle flakes, which are 

 easily reduced to impalpable powder. In the powdered 

 condition in which it is sold it is of a dark ruddy brown 

 colour, and possesses a characteristic, rather offensive 

 odour. It can be kept indefinitely without decomposing, 

 but if allowed to become damp is liable to ferment. It 

 is easily distributed, but is liable to be blown away, and 

 should therefore be mixed with some damp soil before 

 it is spread on the land. It is sold in -two qualities des- 

 cribed as " low dried " and " high dried " respectively. 

 The former contains about 14 per cent, of nitrogen, does 

 not keep so well, but is the more active and cheaper 

 form. The high dried quality contains a smaller pro- 

 portion of water, an'd therefore more nitrogen usually 

 about 16 per cent. keeps better, but is not quite so 

 readily available, and is considerably more expensive, i.e., 

 it costs more per unit of nitrogen. This is due to the 

 fact that as the drying proceeds it becomes more and 

 more difficult to expel the remaining water without car- 

 bonising the organic matter. If over -heated, it acquires 

 a brown or singed appearance, loss of nitrogen results, 

 and the remainder is probably r^nderod less readily 

 available. 



As the nitrogen in dried blood is not directly available, 

 it should be applied fairly early in the spring. For the 

 same reason it is best adapted for use on light soils, for 

 which it is very suitable as there is no danger of loss in 

 wet weather. Under favourable conditions it acts very 

 quickly, i.e., as compared with hair, horn, etc., but its 

 action is slow compared with that of nitrate of soda. It 

 is not so suitable as the last mentioned substance for 



