On the Erythric Acid, Be. 45 
if I may use the expression, a secretion which in company with 
the erythrats of iron often tinges blue. It is with much reason 
that the alkalies make this colour appear, as they expressly pro- 
mote such a secretion, which in their union with erythric acid is 
accustomed to manifest itself by a rose colour. 
37. It is very probable that the alkalies with erythrats of iron 
may constitute triple salts; this may also happen with other 
metallic erythrats, as will presently appear. The triple prussiat 
of potash and the decoction of galls discover iron, from the ery- 
thric solutions producing the customary colours*. s 
Erythrat of Lead, 
38. I have already observed that the erythrat of potash de- 
composes the solution of lead, and forms a white precipitate. 
A similar precipitate is likewise obtained from the same solution 
decomposed by the erythrat of potash, in which the acid is said 
to be altered. We shall now see if we can directly obtain these 
two different species of erythrat of lead, which will confirm our 
opinion on the mode with which erythric acid acts with bases. 
39. Pouring erythric acid on litharge, it is only necessary te 
agitate them a little in order to produce their combination. 
Thick clouds are seen in the liquid, and the erythrat of lead, 
which is precipitated, is insoluble in acetic acid, and even in an 
excess of erythric acid itself. If this erythrat of lead be decom- 
posed by sulphat of iron, and potash be afterwards added to it, 
the blue colour is cbtained. 
_ 40. But if the turbid fluid obtained by agitating erythric acid 
with litharge be exposed to heat, after a slight ebullition the tur+ 
bidness disappears, and the solution assumes a red colour. Con- 
tinuing to boil it, the turbidness returns, and deposits a white 
powder, which is the erythrat of lead in which the acid is altered. 
‘The red liquor has a considerable quantity of it.in solution, but 
simple water dissolves much less; therefore the red liquor with 
the addition of sulphat of iron and potash gives the blue colour, 
which is not produced by the aqueous solution. 
41. From the second erythrat of lead may be extracted that 
acid which is generated at the expense of the erythric. This salt 
miay be decomposed with dilute sulphuric acid in such a manner 
* Whence is it that muriatic or hydrochloric acid, boiled on the most pure 
ric acid, gives a blue colour with triple prussiat of potash to such a degree 
as to create the belief that urtc acid always contains iron? Can it ever be 
that these two acids should produce the same blue substance which was 
ebserved in the erythrats of iron? [shall only observe that Schevle’s as- 
sertion of muriatic acid boiling on uric acid without any alteration, does not 
seem very correct. If the experiment be made, it wili be found that caustic 
potash will devélop from uric acid a very distinat odeur of ammonia, which 
is a proot of its being In some degree altered. 
that, 
