azone in
presence of acetic acid, and (b) as phloroglucide in presence of HCl
(12 p.ct). In (a) by varying the weights of known quantities of
furfural, and using the factor, hydrazone x 0.516 [+ 0.0104] in
calculating from the weights of precipitates obtained, the maximum
variations from the theoretical number were +1.71 and -1.74. In (b) it
was found necessary to vary the factor from 0.52 to 0.55 in calculating
from phloroglucide to furfural. The greatest _total_ range of variation
was found to be 2.5 p.ct. The phenol process is therefore equally
accurate, has the advantages above noted, and, in addition, is less
liable to error from the pressure in the distillates obtained from
vegetable substances of volatile products, e.g. ketonic compounds,
accompanying the furfural.

This method has been criticised by Helbel and Zeisel [Sitz.-ber, Wiener
Akad. 1895, 104, ii. p. 335] on two grounds of error, viz. (1) the
presence of diresorcinol in all ordinary preparations of phloroglucinol,
and (2) changes in weight of the precipitate of phloroglucide on drying.
The process was carried out comparatively with ordinary preparations,
and with specially pure preparations of the phenol. The quantitative
results were identical. The criticisms in question are therefore
dismissed. Although the process is to be recommended for its simplicity
and the satisfactory concordance of results it is to be noted that it
rests upon an empirical basis, since the phloroglucide is not formed by
the simple reaction 2 [C_{5}H_{4}O_{2} + C_{6}H_{6}O_{3}] - H_{2}O =
C_{22}H_{18}O_{9}, but appears to have the composition
C_{16}H_{12}O_{6}.

In part ii. of this paper the author discusses the question of the
probable extent in the sense of diversity of constitution of
furfural-yielding constituents of plant-tissues. Glucoson was isolated
from glucosazon, and found to yield 2.9-3.6 p.ct. furfural. Gluconic
acid distilled with hydrochloric acid gave traces of furfural; so also
with sulphuric acid and manganic oxide.

Starch was oxidised with permanganate, and a mixture of products
obtained of which one gave a characteristic violet colouration with
phloroglucol, with an absorption-band at the D line. On distilling with
HCl furfural was obtained in some quantity. The product in question was
found to be very sensitive to the action of bases, and was destroyed by
the incidental operation of neutralising the mixture of oxidised
products with calcium carbonate. I