On the Erythric Acid, &e. 39 
its colour, and furnishes a fluid of a faint rose colour, and of a 
sweetish taste, which does not render Jime-water turbid. 
9. 'The red erythric acid in more or less time loses its colour, 
and in its stead usually yields white flakes. But if in obtaining 
the redness the heat be stronger than necessary, the red erythric 
acid changes colour much more easily and becomes yellow. This 
change, indeed, takes place instantaneously with the prolonged 
action of the fire; a strong smell of bitter almonds is then 
evolved, which is communicated to water in which the residuum 
is dissolved. | This proves that carbon, azote, and hydrogen, as 
was easy to be imagined, enter into the composition of erythric 
acid. t 
10. The circumstances therefore of the formation of erythric 
acid not only induce the belief that it also contains oxygen, but 
that it contains it in an abundant quantity, so much and so rapid 
is the decomposition of nitrous on uric acid required to produce it. 
Moreover, it appears from the circumstances already mentioned, 
that the erythric acid acquires the red colour in consequence of 
a slight change effected in some one of its constituent parts, in 
which likewise water necessarily concurs. These considerations 
led me to try the action of the Galvanic pile on erythric acid, 
hoping by such means to throw some light on the unknown che- 
mical changes that accompany the formation of the red colour. 
Effect of the Galvanic Pile on Erythric Acid. 
11. The pile which I used consisted of sixty pair of metallic 
plates with a superficies of two inches and ahalf square. At the 
negative pole a tumbler filled with a solution of erythric acid was 
placed, and another with distilled water at the positive pole. A 
platina wire communicating with the respective poles was im- 
mersed in the tumblers, between which passed a piece of amianth 
moistened with distilled water. The electric current was scarce! 
put in motion, when a phenomenon appeared which anaieated 
that this experiment should succeed in the highest degree. Many 
bubbles of gas arose from the positive pole where the water was, 
and none, or scarcely one, and that with difficulty, issued from the 
other pole with the erythric acid. After about an hour the acid 
began to become yellow, and with the usual gradation of colour 
observed when the fire acted on it: finally, it acquired a deep red 
colour. After some time the disengagement of gas appeared 
copious even at the negative pole, but never so much as it was 
at the other. Although the erythric acid was become of a deep 
red colour, yet there existed a great quantity unaltered in the 
solution, but which after twenty-four hours was considerably 
‘iminished in volume. A portion also of the erythric acid was 
transported to the positive pole, as was indicated by lime-water. 
, The 
