6 DR. ANGUS SMITH ON THE COMPOSITION 
decomposed; a blueish scum appears on the liquid, and 
the sides of the vessel are covered with fine crystalline 
needles which have a blueish appearance. This substance 
I have only a very small portion of, but may obtain more 
for a future occasion. 
If a colour should be found identical with Runge’s, I 
should call this acid pic-erythric acid. The colour which 
this substance always assumes appears to establish an 
essential difference between it and the acid obtained by 
Runge, but its action with bases is still more widely apart. 
Runge says that it unites with mordants. I have thrown it 
down with oxides of tin and iron, alumina and other bases, 
but have found that it has by no means a power of re- 
taining hold of the base. The colour of these compounds 
on cotton is certainly very beautiful for a short time, but 
carbonic acid or a weak alkali removes it rapidly. It 
could never, therefore, be used as Runge’s substance to 
form a dye, or it might be obtained in very great abun- 
dance, and at a very cheap rate, in all gas-consuming 
towns. Another reason why it could not be used as such 
is that its pecaliar rosy colour is only developed by al- 
kalies ; the alkalinity being removed, it is a dull resin 
again. This occurs very readily, the carbonic acid of the 
air being sufficient for the purpose. The magnificent 
colour of the lime compound is therefore very fugitive. 
If used to dye silk or wool, it imparts, if in an alkaline 
state, the same magnificent colour as to cotton, but the 
same evanescence is soon proved, and the cloth appears 
of a dirty brownish hue. 
Runge says also that it can be used as a pigment. But 
of itself it has no beauty. Its salts also fail as a pigment, 
from the reasons above given. The lime salt, for example, 
which would be the most beautiful for the purpose, must 
be kept strongly alkaline, as the carbonic acid of the air 
readily reproduces the dark and dirty brown. I consider 
