Analyses of Ashes of Plants. 
667 
It will be seen that the first named, silica, constitutes only a 
very small proportion of the whole ash; it probably exists only in 
the skin as a mechanical protection to the e;rain ; in quantity it 
varies between the limits of TSO and 6 00 per cent.; in one 
instance however the ash contains as much as 9 71 per cent, of 
this substance, Spec. 29. I'he specimen in which this unusually 
large quantity of silica occurs, is also remarkable for the very 
large proportion of oxide of iron present hi its ash ; it was grown 
on the " green-sand," and hence in all probability the peculiarity 
referred to. The green-sand owes its colour to the large quantity 
of silicate of protoxide of iron existing in it. When decomposed 
by liming, or water containing carbonic acid, it would furnish an 
abundant supply of both these substances, which would pass into 
the plant. The average proportion of silica in the ash of wheat 
upon the 28 specimens in the table is 3-66 per cent. 
Phosphoric acid, the next body in the table, is certainly the 
most important of all the mineral ingredients of wheat, both on 
account of the large proportion of it which exists in the ash, and. 
the very small extent to which it is present in soils. 
The ash of wheat contains a quantity of this substance, varying 
between 40 and 50 per cent, of its weight. In one specimen how- 
ever (No. 37) the phosphoric acid does not exceed 35 per cent. ; 
but this result does not accord witli any other we have obtained. 
The specimen alluded to is from Marianople; it is in peculiarly 
small and thin grains, almost approaching in appearance those of 
rye ; it is of interest also in containing a large proportion of soda, 
not in the place of potash, but in addition to the usual amount of 
the latter alkali. Specimens 41 and 43 exhibit the highest 
amount of phosphoric acid in any of the ashes. The mean of 
phosphoric acid in all the specimens is 45'00 per cent, of the ash.. 
A bushel of wheat of 61 Ibs.^ containing T67 per cent, of mineral 
matter, would require 7to oz., or taking 28 bushels an acre as an 
avei age, we should remove from the soil in the grain of every acre 
of wheat 12 lbs. 3 oz. ^Ilie largest amount removed in any crop 
examined is seen in specimen 47, where it reaches 22 lbs. 5 oz. 
This sample has been before noticed, from the large amount of 
ash taken off in the straw; it is in all respects an extreme case, the 
ash of the grain, the straw, and the chaff, being all unusually 
high. The large amount of crop with these high per centages 
renders the specimen the most exhausting of all those which have 
fallen under our notice. 
Sulphuric acid is generally present in the ash of wheat, though 
in small proportion ; it docs not exceed in any instance 2*00 per 
cent., and is usually much less than this. The mean quantity of 
this acid in the ash is 0 34 per cent., and the largest amount 
removed by an acre of wheat (in this grain) 8 oz. 
VOL. VH. 2 V 
