472 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON 
in the manner just indicated, a pot of soil, prepared exactly as for an experiment with a 
plant, was submitted to the same conditions of air, temperature, moisture, &c., as the pots 
containing the experimental plants. The result was, that there was no accumulation of 
combined Nitrogen. The result with the matrix of pumice also showed, compared with 
that of the soil-matrix, that no error was to be feared from the influence of the latter in 
absorbing and retaining combined Nitrogen already in connexion with the plant. 
For our purpose, pure volcanic pumice was used. It was powdered until the mass was 
quite fine and the largest pieces were about the size of peas. ‘This powder was subjected 
to long washing in the same manner as the ignited soil. Lastly, it was dried ready for 
a final ignition before being used. 
B.—The Mineral Constituents added to the prepared Soil. 
In most cases the necessary Mineral Constituents were supplied in the form of the 
ash of the plant of the description to be grown. In a few instances, where this was 
not practicable, the ash of some other plant was selected. Weak solutions of sulphates 
and phosphates, as well as ash, were also sometimes used. 
In some instances the ash was obtained by burning a quantity of the entire plant 
when in seed. In other cases, the seed and the rest of the plant being burnt separately, 
a mixture of the two ashes was made in such proportion as to represent the composition 
of the ash of the entire plant. 
Thus, in the experiments of 1857, for Wheat a mixture of one part of the grain-ash 
and six parts of the straw-ash, for the Barley a mixture of one part of the grain-ash 
and three parts of the straw-ash, and for Beans a mixture of one part of the corn-ash 
and two parts of the straw-ash was used. In the experiments of 1858, the ash used for 
these crops was obtained by burning the entire plant. For Clover, the ash of Clover- 
hay was employed. 
In some instances of Leguminous plants the ash was saturated with sulphuric acid, 
and then ignited, before being used. 
Each ash was burnt in a large shallow platinum dish, heated in a current of air, in 
a cast-iron muffle. The burning was continued until all coaly matter had disappeared. 
The ash was then preserved, but was always submitted to a final ignition before being 
used. Examination failed to detect combined Nitrogen in any of the ashes so prepared. 
In order that the roots of the plants should find an abundance of mineral matter at 
the most active period of growth, it was desirable that the matrix should contain as 
much of such matter as was consistent with healthy development. A consideration of 
the chemical constitution of soils suggested a proportion of 0-8 to 1:0 per cent. of ash; 
and this was the quantity added to the matrix for the experiments of 1857; but for 
those of 1858 only about half as much was employed. 
