On the Erythric Acid; &c. 27 
Parr I],—Having intimated the discovery of anew acid in the 
preceding part of this memoir, thanks to the care with which my 
father superintends my studies, 1 am now enabled to describe it 
more completely. This acid, as already observed, originates 
from the action of nitrous on uric acid, and is distinguished by 
the singular property of reddening when exposed to heat; for 
this reason I propose to call it erythric, from 2guégaivew, toredden, 
I now proceed to describe the properties of this new substance, 
but must observe, and regret, my imperfect success, as it is a com- 
pound which often changes and readily becomes of a quite dif- 
ferent nature; and hence my disappointment in sometimes not 
being able to give an exact account of all the phenomena, and 
sometimes being obliged to abandon certain subjects without any 
research, to avoid entering into a too extensive and difficult field, 
Nevertheless, I hope that my observations will he of some utility 
to those who may subsequently examine this complicated subject 
under more favourable circumstances. 
Mode of obtaining the Erythric Acid. 
1. 1 have already related Bergman’s observations on the rapid 
decomposition and deposit obtained by pouring nitrous acid on 
uric acid or urinary calculi. That deposit is the erythric acid, 
which I found disposed in regular figures; and to obtain it pure, 
the following is the easiest process to be adopted. Unite in the 
manner before mentioned the nitrous and uric acids; leave the 
mixture at rest until the numerous floating yellow flakes have 
settled at the bottom of the receiver ; then pour off the liquor, 
collect the solid part on blotting paper, and dry it as much as 
possible ; afterwards dissolve it in water, and evaporate it slowly 
im the airs by this method most beautiful crystals of pure ery- 
thric acid may be obtained. ‘Fhis liquor transmits nitrous va- 
pours, and also contains erythrie acid in solution. 
2. Chlorine, iodine, and oxalic acids with uric acid can give 
origin to this new acid. Put uric acid in a bottle full of chloric 
gas, it will instantly be decomposed, and a substance which 
tinges the skin of a lively red colour will be produced. In like 
manner, a mixture of uric acid with iodine, or with oxalic, acid 
exposed to the action of heat, a decomposition is seen to take 
place, and finally a bright rosy residuum is. produced. This 
appearance of colour indicates the formation of erythric acid, 
Characters of the Erythric Acid. 
3. The crystals of erythric acid have a rhomboidal form, are 
colourless and perfectly transparent ; their taste is at first pun- 
gent, and afterwards becomes sweetish; exposed to the light of 
the sun they redden, and preserved in paper they impart to it 
C3 mally 
