458 



Messrs. A. D. Hall and C. G. T. Morison. [Dec. 22, 



by the soda of the sodium silicate. The beneficial effect of the sodium 

 silicate is chiefly shown on Plots 1 and 3, and there is little gained by its 

 use on Plots 2 and 4. Now Plot 3 is abundantly supplied with alkaline 

 salts in the shape of sodium nitrate and sulphates of sodium, potassium, 

 and magnesium, so the addition of a further supply of sodium in sodium 

 silicate would not be likely to produce any effect. Eather, if the sodium 

 were the active constituent, would its effect be seen on Plot 2, which 

 receives no alkaline salts beyond the sodium in the sodium nitrate common 

 to all the plots. The notable fact is that the effect of the sodium silicate 

 is seen only on ' the two Plots 1 and 3 suffering from phosphoric acid 

 starvation, because they have been cropped for so many years without 

 the application of any phosphates. The silica, in fact, would seem to 

 partially replace or to do the work of the superphosphate supplied to 

 Plots 2 and 4. 



Such an opinion, derived from the yield, may be confirmed by an examina- 

 tion of the plots when approaching ripeness. The most striking feature 

 at that time is the deferred maturity of the barley on the plots without 

 phosphoric acid ; they remain of a greener colour, and are still erect at a 

 time when the barley on the normal plots has turned down and begun to 

 yellow for harvest. This ripening effect of phosphoric acid finds a parallel, 

 though to a smaller degree, on the half plots receiving sodium silicate. 

 On Plots 1 and 3, which are without phosphoric acid, the portions receiving 

 sodium silicate are always riper by a few days than the other halves which 

 get neither phosphoric acid nor silica. 



A series of analyses of the ash of the barley grown on these plots in 

 1903, a wet and sunless year, and 1904, a normally warm season, also serve 

 to strengthen the idea that the action of the silica is in some way bound 

 up with that of the phosphoric acid in the plant. Table III shows the 

 percentages of phosphoric acid and silica in both grain and straw on the 

 four plots, each of which is subdivided so as to be with and without silica. 



It will be seen that the lack of phosphoric acid in the manure applied to 

 Plots 1 and 3 is reflected in the diminished proportion of phosphoric acid in 

 the ash of the grain, and still more in the low percentage present in the ash 

 of the straw. "When sodium silicate is added to the plots without phosphoric 

 acid the proportion of phosphoric acid in the grain ash rises, but simul- 

 taneously it falls in the straw ash. 



On the plots receiving phosphoric acid the silicate does not always cause 

 an increase in the percentage of phosphoric acid in the grain ash, though as 

 before it generally diminishes that in the straw ash. 



On all the plots the sodium silicate causes an increase of silica in the ash 



