Analyses of the Ashes of Plants. 
153 
inasmuch as it is supposed to be a measure of the organic acids 
in combination with the different bases before combustion. We 
may shortly consider what is the probability that, by the usual 
methods of burninsf, uniform results should be obtained in regard 
to the quantity of this acid. In the case of silicious ashes it must 
be at once allowed that there is no hope of so regfulating the 
temperature to which the ash is exposed as to avoid the displace- 
ment of carbonic acid to a greater or less extent by the more 
powerful silicic acid. It is, we believe, verily impossible at any 
available temperature to burn a silicious vegetable, such as wheat- 
straw or barley-straw, to a moderately white ash without action of 
this sort; the silica is so finely divided, and, as the process ad- 
vances, so intimately mixed with the other constituents, that an 
alteration from the cause in question is unavoidable ; indeed, the 
absence of carbonic acid in any quantity in nearly all reported 
analyses of plants in which silica is an important constituent, and 
the necessity which analysts always experience of subjecting a 
sdicious ash to particular treatment to decompose insoluble 
silicates, are indirect proofs of the justice of this statement. 
It must then, we believe, be admitted that no coincident results 
in the quantity of carbonic acid are to be looked for in the case of 
silicious ashes by the ordinary methods of burning. 
The question next presents itself — does the careful prepa- 
ration of non-silicious ashes give uniform results in regard to 
carbonic acid, and is it possible to use these results as data in- 
dicative of the proportion of organic acids existing in the plants 
before incineration ? 
In the absence of silica, which is the only uncombined mineral 
acid in plants, we should suppose that no other constituent would 
be liable to vitiate the determination of carbonic acid, were it not 
that phosphoric acid combines in different proportions Avith bases, 
and, until it has reached its point of saturation, may be supposed 
to be capable of acting as an acid. 
The point to be decided is — are phosphates containing less 
than three proportions of base capable of attacking carbonates 
and driving off the carbonic acid ? In proof of the affirmative 
answer to this proposition. Rose has quoted the experiments of 
Golding Bird, who produced the basic phosphate of soda 
(3 Na O + P O5) by heating to redness a mixture of the ordi- 
nary phosphate of soda with acetate of soda. The following ex- 
periment by ourselves is confirmatory of Rose's statement : — 
40-64 grains of pyrophosphate of soda, strongly dried, were 
mixed with 53-30 grains of pure carbonate of soda (also strongly 
heated). A gentle heat was applied to the mixture by a gas-flame ; 
it lost 3-83 grains; by a second heating at a higher temperature 
in a lurnace, the salts being in partial fusion, 2 grains more were 
