38 On the Erythric Acid, Sc. 
many reddish spots ; exposed to heat they decrepitate, and also 
assume a red colour; left in contact with “dry air, they efforesce, 
lose their transparency and become white. When found in this 
state they do not redden on exposure to the solar light; and if 
deprived of their water of crystallization, and exposed to the fire, 
they become yellow, and burn without reddening. Hence'we 
may observe, that the presence of water is necessary in order to 
their becoming red. 
4. The crystals of erythric acid are very soluble in water and 
in aleohol, without either impairing the transparency or changing 
the eoleilr of those fluids. The watery solution has a sweetish 
taste, no smell ; but it appears that it acquires a smell in time, 
which may be the index of its being about to undergo some al- 
teration. It reddens the blue tincture of vegetables, and théir 
colour may be restored by the alkalies. Lime-water becoming 
turbid discovers the presence of the smallest quantity of erythric 
acid. 
5. The solution of erythric acid by spontaneous evaporation 
in the shade, crystallizes again without being altered: but if 
rapidly evaporated it becomes a solid red coloured mass, which 
is revived on dissolving in water, of which it colours a great 
quantity. In like manner the erythric liquid tinges the skin 
and other bodies red, more promptly than usual with the common 
solution of uric in nitrous acid. 
6. To discover if in the act of changing any peculiar substance 
was evolved, the erythric acid was distilled with a strong fire. 
It does not hoil out at a high temperature. Towards the con- 
clusion of the evaporation, it became yellowish, afterwards red ; 
but no product could be found in the simple water which was 
distilled. 
7. In the solution of erythric acid héaaehba at the fire, a small 
portion only of the acid suffered change. In fact, the smallest 
drop renders turbid a great quantity of lime-Wwater and if by 
evaporation the solvent water is diminished, we see the erythric 
acid depositing itself. It is not, however, the same when the 
red solution is obtained by washing the spots left by erythric acid 
en the skin, cloth, &c.; in this vase the erythric acid appears 
almost entirely altered, and lime-water scarcely discovers its 
existence, presenting after some time a thin net on its surface. 
8. The cclouring matter which reddens the erythric acid may 
he dissipated by heat. In fact, if the erythric acid be reddened 
in a watch- -glass over the fame of alamp, “afterwards dissolved in 
water and again exposed to the same heat, beautiful red vapours 
are seen rising, particularly at night, and the fiuid loses its co- 
lour. This fluid is found to be erythric acid, which may be again 
reddened, If the red liquor b e rapidly heated 3 in a retort, it loses 
its 
