Mineral Manures and Manuring. 
281 
mixture of phosphates, potash-salts, and dung. Phosphates ah)ne 
are not sufficient, for light soils are generally deficient in 
alkalies as well as phosphates. They are frequently too poor 
in mineral food to make use of even the amount of nitrogen 
contained in a small dressing of dung. Consequently this 
nitrogen is lost, being washed out of the soil, in the form of 
nitrates, by every continuous rainfall. 
At one time it was believed that the water contained in the 
soil was capable of dissolving a sufficient quantity of mineral 
matter to supply plants with their mineral food, and also that 
this was the only means by which such mineral food was 
obtained. Liebig has shown, however, that this is not the case. 
Plants take up three-fourths of their mineral food directly from 
the soil itself, by means of the constantly growing and newly 
formed tips of their rootlets. Voelcker has also shown how 
small are the quantities of phosphates which pure water dis- 
solves ; thus he found that 70,000 lbs. of pure water dissolved of — 
Lbs. 
Precipitated phosphate of lime burnt and finely ground 2 '20 
„ „ „ precipitated and still moist 5 "56 
„ „ magnesia burnt and powdered 7 " 04 
„ „ ,, precixjitated and still moist .. .. 14 "36 
„ „ lime with 1 per cent, ammonium carbonate 11 "28 
„ ,, ,, 1 „ nitrate of soda .. .. 6*88 
Pure bone-ash from hard bone 1 • 18 
American bone-ash 1*88 
Monk's Island phosphate I'OO 
Sombrero phosphate 0"84 
Coprolites 0-64 
Estremadura phosphorite O'lO 
Norwegian apatite 0*44 
Peruvian guano 2 • 52 
From these figures we learn that the calcium phosphate of 
Peruvian guano, and of burnt bones, is far less soluble than 
precipitated phosphate. It is otherwise with bone-meal and 
steamed bone-meal, of which 5*4 lbs. and 5-9 lbs. respectively 
were soluble. This is due to the formation of ammonia and 
organic acids by the decomposition of the gelatine contained in 
the bones, for these substances facilitate the solution of phos- 
phate of lime. In the same way a small amount of oxalic acid, 
which exists in guano, increases the solubility of a portion of 
its phosphate. Ammonia, apart from its stimulating effect upon 
the growth of the plant, is also a powerful aid to the solution of 
the phosphates. Hence the influence which bones and guano 
exert, and when these are used as manures the roots of the 
plants have not to first seek the phosphoric acid and then the 
