76 
MR. STENHOUSE ON THE EXAMINATION OF THE 
of picro-erytlirin are generally speaking very correct, but he has fallen into one or 
two errors. Mr. Schunck supposes that picro-erytbrin is formed from erythric acid 
by that acid merely taking up five equivalents of water. Now, I have fully ascertained 
that erythric acid is never converted into picro-erythrin without the evolution of a 
considerable amount of carbonic acid gas, so that in this process carbon is always 
eliminated, and the change is not produced merely by the absorption of the elements 
of water. Picro-erythrin is a very stable body; a quantity of it after being boiled 
in water for thirty-six hours had undergone very little change, a very small portion 
of it only having been converted into orcin, and probably into pseudo-orcin. Mr. 
ScHUNCK asserts that when picro-erythrin is boiled with an excess of lime or baryta 
it is wholly converted into orcin. A small quantity of orcin is always produced by 
this process, but the great bulk of the compound then formed is a new sweet crystal- 
lizable body to be described in the next section, and which I shall call pseudo-orcin. 
Pseudo-orcin. 
I have as yet only succeeded in obtaining this very curious substance from erythric 
acid and its compounds, by acting on them with alkalies. As already mentioned, it is 
only from picro-erythrin itself, or from the portion of erythric acid which yields picro- 
erythrin, that pseudo-orcin is obtained. Erythrelesic acid does not yield a trace of it. 
The best way of preparing pseudo-orcin in quantity is the following. The lime solu- 
tion of the Roccella Montagnei should be boiled in an open pan for two or more hours, 
and the liquid concentrated to a third or a fourth of its bulk. A stream of carbonic 
acid gas should be sent through the liquid so long as carbonate of lime is preci- 
pitated, and the liquid filtered and evaporated on the water-bath to a thick syrup. 
This syrup consists chiefly of orcin and pseudo-orcin, with much reddish colouring 
matter containing a good deal of resin. The syrup should then be introduced into 
a flask, and treated with a large quantity of ether, which dissolves the orcin and most 
of the colouring matter, leaving the pseudo-orcin undissolved. A more economical 
proceeding is to mix the syrup with three times its bulk of alcohol. After standing 
for a couple of days the pseudo-orcin crystallizes out in small shining crystals. These 
crystals should be collected on a cloth filter, pressed, and wasiied with cold strong 
spirits, which removes most of the colouring matter and any adhering orcin. On 
being crystallized twice or thrice out of strong boiling spirits, the pseudo-orcin is 
obtained in large shining colourless crystals. Pseudo-orcin may be obtained in still 
finer crystals by crystallizing it out of water, in which liquid it is exceedingly soluble, 
much more so than in spirits. I have obtained it from its aqueous solutions in 
curiously truncated pyramids, nearly an inch broad, having a brilliant diamond 
lustre. In fact, there are very few organic substances which form more splendid 
crystals than pseudo-orcin. I sent a quantity of these crystals to Professor Miller 
of Cambridge, who was so kind as to determine their measurements and optical pro- 
perties. The following are the results of his examination ; — 
