on treating Uric with Nitrous Acid, &ec. 35 
form conjectures on the different appearances of colour, or the 
different odours, which are developed during the process. It 
would be equally difficult to ascertain, that with the same ele- 
ments of these substances there may not be formed, and after- 
wards destroyed, other peculiar combinations: The animal sub- 
stances are endowed with so much mobility, and suffer such no- 
table alterations in consequence of a small change in their parts, 
although imperceptible to the senses, that we need not be sur- 
prised if in this case some of them should have eseaped our at- 
tention. But without digressing from my subject, I can adduce 
examples in which nature betrays herself, and reveals in the mean 
time that in the course of her operations important changes are 
effected. These facts will not be reluctantly learned while they 
are accompanied by many interesting phenomena. 
It it well known that the solution of uric in dilute nitric acid, 
reduced to dryness and heated, has the property of communi- 
cating to bodies a deep red colour. This dye is therefore very 
soluble in water, and we may obtain from it a beautiful liquor 
of alight ruby colour*. Being provided with an abundant quan- 
tity of this liquor, I evaporated it to obtain the colouring mat- 
ter in a solid state. At a certain period of the process, the fire 
becoming somewhat strong, the rosy colour in an instant disap- 
peared, and was succeeded by a yellowish hue. This change has 
occurred every time I repeated the experiment. It appears 
that in this case even the water had a part, since we-know by 
other means this colouring matter may be obtained unaltered in 
asolid state. In seeking to discover some means of restoring 
the faded colour, I found that potash, ammonia, and lime an- 
swered this purpose, only the colour reproduced was more rosy 
and delicate. The potash in the smallest quantity produced the 
effect better than the others. In like manner it at the same 
time yielded a rosy precipitate, which when left to repose at- 
tracted all the colouring matter, and the solution remained. dis- 
coloured and alkaline. If, when the precipitate is immediately 
formed, it be collected on a filter and dried, it retains a delicate 
rose colour, interspersed with very minute shining points. Those 
points, which have a most agreeable effect in the light of the sun, 
are found even beyond the space where the colour extends. Lime 
yields a deeper colour, and when colJected on the filter has the 
appearance of velvet, and also presents brilliant points. 
* T have almost always used the washings of the red spots left on the 
skin by the above solvtion, and it is often very deep. The red residuum 
which is obtained by the heat of the fire makes the washing’s naturally more 
easy to be changed, or to differ from themselves. It is remarkable that such 
red liquors, when slowly evaporated, yield prismatic crystals, and dissolving 
anew in water, we again obtain a reddish liquor. i 
C2 Desirous 
