mOPERTIES OF BONE-DUST. 277 



Their effect upon the produce of potatoes and of cereals 

 on sucli fields is equal to that of Peruvian guano. For 

 turnips and rape, which derive advantage from the pre- 

 sence of sulphuric acid, they have a special value. 

 On chalky soils, the free phosphoric and sulphuric acids 

 are immethately neutrahsed, by which they are deprived 

 of one of their essential properties, viz., their ready 

 diffusibility, which renders them so valuable a manure 

 for other soils. 



Among the neutral phosphates bone-dust holds the first 

 rank. When bones are exposed, under higli pressure, to 

 the action of steam, they lose their toughness, and swell 

 up into a soft gelatinous mass, which, after dryhig, may 

 be readily ground to a fine powder. In this form it 

 spreads, with great rapidity, through the soil ; it dissolves 

 in water to a small but perceptible extent, without requir- 

 ing the presence of any other solvent. What dissolves, 

 under these circumstances, in water, is a combination of 

 gelatine with phosphate of hme, which is not decomposed 

 by the arable earth, and therefore penetrates deep into 

 the ground — a property wanting in the superphosphate. In 

 the moist ground, however, the gelatine speedily putrefies, 

 being converted into ammonia compounds, and the plios- 

 l)hate of hme is then retained by the arable earth. Bone- 

 dust is the agent best adapted to supply phosphate of 

 lime to the deeper layers of the arable soil, for which 

 pui-j^ose the superphosphates are not suitable. Bone- 

 earth, or bone-ash, is the name applied to bones freed, by 

 calcination, from the glue or gelatinous part. The animal 

 charcoal of sugar refineries belongs to this category. 

 It must be reduced to tlie finest powder to render 

 it fully available for manuring purposes. To effect 

 its more speedy distribution through the soil, the pre- 

 sence of a decaying organic substance is necessary to 



