394 
MR. STENHOUSE ON THE EXAMINATION OF THE 
of the moisture it contained had been removed, it was found advisable to treat it for 
a short time with a small quantity of dilute spirits of wine at nearly a boiling tempe- 
rature. This had the effect of freeing it from a greenish-coloured resinous substance. 
The undissolved portion of the precipitate, whicli had now become much whiter, was 
next digested with strong alcohol and a considerable quantity of purified animal 
charcoal, great care however being taken to prevent the liquid from boiling. The 
solution was then filtered, and on standing for some hours the colouring principle 
was deposited in small prisms arranged in stars. By repeated digestions with alcohol 
and animal charcoal it was rendered colourless, when it had a silky lustre. A con- 
siderable portion of the original precipitate however did not dissolve in the alcohol, 
and consisted of a brownish coloured humus-like substance. 
The colouring principle of the Gyrophora pustulata, which I shall call gyrophoric 
acid, when pure forms small white soft crystals, which have neither taste nor smell. 
It is almost insoluble both in cold and in boiling water. It is also but sparingly 
soluble both in ether and in alcohol. It is much less soluble therefore in hot alcohol 
than either orsellic, lecanoric or erythric acids. Its solutions have no action upon test- 
paper. Gyrophoric acid has no saturating power, for the smallest quantity of either 
potash or ammonia gives its solutions an alkaline reaction. When gyrophoric acid 
is boiled for a short time with a considerable excess of any of the alkalies or alkaline 
earths, it gives off carbonic acid and is converted into orcine. When, on the other hand, 
it is boiled with a very small portion of alkali only, it is decomposed in the same way 
as the orsellic, erythric and other similar acids, and yields a corresponding interme- 
diate acid, which is more soluble in water and exhibits more distinctly acid properties 
than the gyrophoric acid from which it has been derived. Gyrophoric acid strikes the 
same bright red fugitive colour with hypochlorite of lime which appears to be charac- 
teristic of this class of colouring matters. The red solution which it yields is how- 
ever rather more durable than those of the above-mentioned acids. Gyrophoric acid 
is very slightly soluble even in a large excess of a cold aqueous solution of ammonia, 
and it is precipitated by ammonia from its alcoholic solution, without however com- 
bining with any of that alkali. When gyrophoric acid is heated with an alcoholic 
solution of ammonia it readily dissolves, but at the same time it is decomposed with 
the formation of an intermediate acid. When gyrophoric acid is macerated with an 
excess of ammonia and exposed for a considerable time to the air, it is slowly con- 
verted into a purplish-red colouring matter similar to that which the analogous acids 
furnish in the same circumstances. 
A quantity of gyrophoric acid, prepared in the way already described and repeat- 
edly washed with boiling water to free it from any trace of the ether compound which 
might have adhered to it, was subjected to an analysis : — 
I. 0*2785 grm. substance dried in vacuo, and burned with chromate of lead, gave 
0*621 carbonic acid and 0*123 water. 
II. 0*175 ditto gave 0*3925 Co^ and 0*082 water. 
