284 
Mineral Manures and Manuring. 
phosphate per acre, showed that three-lourths of the phosphoric 
acid remained within the first 9 inches of surface-soil, and one- 
fourth in the next 9 inches. In the third 9 inches no appre- 
ciable quantity above that naturally present in the soil could be 
found, save on those plots Avhich had received at the same time 
1000 lbs. of potassium and sodium-salts. 
Hence it follows that the action of superphosphate, especially 
during the first year, depends not merely on the quantity applied, 
but also on the care with which it is distributed in the soil. 
Only by mechanical aids, such as the harrow, can we bring 
the phosphoric acid of superphosphate a few inches deeper into 
the soil, or somewhat deeper still by means of the plough. And 
these are the only means by which we can assist in distributing 
the phosphates and potash-salts applied to the soil. A more 
thorough division and distribution may, however, be obtained 
if the superphosphate before being applied is dissolved in water. 
Professor Voelcker quotes an experiment in support of this. 
Two hundredweights of superphosphate per acre dissolved in 
water before being applied to the land gave the same result of 
turnips as 4 cwts. strewn broadcast over the ground and harrowed 
in. In the latter case much of the superphosphate remained 
unchanged upon the surface until dissolved by heavy rain. Not 
until then was the phosphoric acid precipitated by the surround- 
ing soil. Even after six weeks, particles of superphosphate were 
found still acid and consequently unchanged. This explains 
the feeble action which superphosphate sometimes exhibits in 
dry weather. 
• >' The reason why we dissolve all phosphates, even bone-meal, in 
acid, is not that they may become more soluble in water and 
remain so, but that by subsequent precipitation they may be 
brought, firstly, into a finer state of division than can be obtained 
by any mechanical means ; and secondly, because when in this 
state they are easily acted upon by organic acids. Freshly pre- 
cipitated tribasic calcic phosphate is easily soluble in acetic 
acid, just as the dibasic phosphate is soluble in ammonium 
citrate ; but bone-ash and bone-meal are no more attacked by 
these reagents than mineral phosphate is. Many practical and 
experienced agricultural chemists, therefore, consider that the 
so-called reverted phosphates, which occur in superphosphates 
made from phosphorite, as well as all other precipitated phos- 
phates soluble in ammonium citrate, may be just as valuable to 
the farmer as soluble phosphate. 
Coarse bone-meal and bones were employed as manure in 
large quantities before 1843, but it was at that time believed 
that gelatine and lime were the fertilising portions. Liebig first 
pointed out that phosphoric acid was the most valuable con- 
