Clover as a Preparatory Crop for Wheat. 
415 
drops of hydrocliloric acid, and the acid solution carefully evapo- 
rated to complete dryness. The hard, dried residue is again 
made acid with muriatic acid, a little water is then added, and 
the liquid passed through a small filter, on which are left inso- 
luble traces of the silica originally thrown down with magnesia. 
A few drops of citric acid having been added to the acid solu- 
tion, with a view of keeping any traces of iron in solution, strong 
ammonia is finally added, which throws down a second time 
phosphate of magnesia and ammonia, now free from silica and 
oxide of iron. The precipitate is collected, washed with am- 
monia-water, dried, burned in a platinum crucible or capsule, 
weighed, and the phosphoric acid calculated from the weight of 
the tri-basic phosphate of magnesia left on burning. 
Following this plan and the precautions here indicated, the 
smallest amount of phosphoric acid in a soil can be determined 
with great precision. If the magnesia precipitate be not redis- 
solved and freed from silica, as pointed out, a higher percentage 
of phosphoric acid necessarily is obtained than the actual quan- 
tity which the soil contains. 
Clover-roots. — The roots from 1 square foot of soil were cleaned 
as much as possible, dried completely at 212^, and in that state 
weighed 240 grains. An acre consequently contained 1493i lbs. 
of dried clover-roots. 
The clover-roots contaiued : — Dried at 212° Fabr. 
♦Organic matter 81-33 
tMineral matter (ash) 18-67 
100-00 
* Yielding nitrogen 1-635 
Equal to ammonia 1 • 985 
t Including insoluble siliceous matter (clay and saud) 11*67 
Accordingly the clover-roots, in an acre of land, furnished 
24^ lbs. of nitrogen. We have thus : 
Lbs. of Nitrogen. 
In the 6 inches of surface soil 3350 
In large clover roots 24a 
In second inches of soil 1875 
Total amount of nitrogen in 1 acre of soil) co^ni 
12 inches deep \ ^ 
Equal to ammonia 63745 
Or in round numbers 2 tons 6 cwts. of nitrogen per acre, an 
enormous quantity, which must have a powerful influence in 
encouraging the luxuriant development of the succeeding wheat- 
crop, although only a fraction of the total amount of nitrogen in 
the clover-remains may become sufficiently decomposed in time 
to be available to the young wheat-plants. 
