86 
MR. STENHOUSE ON THE EXAMINATION OF THE 
and shows that though they differ considerably from each other in some respects, 
still a very intimate relation exists among them. Mr. Schunck first observed that 
when lecanoric or erythric acids are boiled with an excess of any of the alkalies, 
orcin and a carbonate of the alkali are invariably produced. Mr. Schunck was of 
opinion, and in this he has been followed by Messrs. Rochleder and Heldt, that 
orcin and carbonic acids are the only products of this decomposition. We have 
already seen that this decomposition is by no means so simple as these gentlemen 
supposed ; that, first of all, intermediate acids are always formed, and that in the 
case of the erythric and evernic acids, orcin is not the only ultimate product, but 
that pseudo-orcin and evernesic acid are also invariably obtained. Though orcin 
may be procured from (alpha) and (beta) orsellic acids, from erythric acid, and from 
lecanoric and evernic acids, they are not all of them equally suitable for this purpose. 
By far the best way, in fact the only way, of procuring colourless orcin, is to boil the 
(alpha) and (beta) orsellesic acids or erythrelesic acid in water from half an hour to 
an hour, when a great deal of carbonic acid is given ofif, and on the solution being 
concentrated and set aside to cool, abundance of colourless crystals of orcin are depo- 
sited. If a little animal charcoal is kept in the solution while it is being concentrated, 
it will be found useful in preventing any tendency to oxidation. I think it will also 
be found, though 1 have not had the opportunity of trying the experiment, that when 
lecanoric acid is neutralized with lime or baryta and boiled for a short time, it will 
be decomposed like orsellic and erythric acids, and yield an aeid similar to the orsel- 
lesic and erythrelesic acids, which I have no doubt, by simply boiling in water, will 
also be converted into colourless orcin. By long-continued boiling with water, 
(alpha) and (beta) orsellic and erythric acids may no doubt be slowly converted into 
orcin without the intervention of an alkali. An immense amount of boiling is how- 
ever required for this purpose. A quantity of orsellic acid which had been kept 
continuously boiling for three days, was only partially converted into orcin, and the 
product was far from colourless, owing to the effects of oxidation. 
I. 0‘332 grm. colourless orcin, prepared as above described, dried at the ordinary 
temperature, gave with chromate of lead 0‘717 carbonic acid and 0’204 water. 
16 C 
1222-960 
Calculated. 
59-36 
Mr. Schunck’s. 
58-98 
I. 
58-90 
11 H 
137274 
6-66 
7-68 
6-82 
70 
700-000 
33-98 
33-96 
33-96 
2060-234 
100-00 
100-00 
100-00 
It will be seen from this that the faint red colour which orcin has when prepared 
by boiling with an excess of alkali, has no influence upon the analysis. 
When it is wished to prepare orcin on a large scale without its being required to 
be perfectly colourless, the following process will be found very convenient. The 
clear solution obtained by macerating any of the varieties of the. Roccella tinctoria, or 
