180 
Proceedings of the Royal Society 
for in that case the varnish will, in course of time, acquire a much 
browner shade (the oxidised iron urushiate having a reddish brown 
colour), losing at the same time in some measure its admirable 
qualities of resisting the action of strong chemical reagents. A 
small quantity of any soluble iron salt added to the juice will suffice 
for the preparation of the best roiro lacquer. 
Free alkalies impart a very dark colour to the solution of urushic 
acid, which by transmitted light looks purplish blue, and by reflected 
light very dark brown. This viscid compound, if exposed to the air, 
rapidly blackens and dries up. It is a compound of an alkali metal 
with the acid, the normal salt of which will probably be represented 
by the formula C 14 H l7 M'0 2 . The salt was not quite fit for analysis, 
as it seemed to suffer oxidation like some other salts of urushic acid 
during the processes of purification and drying. 
Long-continued action of strong hydrochloric acid upon urushic 
acid produces a peculiar change in the latter ; the resulting body has 
exactly the same composition as the original acid, but very different 
properties. When urushic acid was heated with a very large excess 
of hydrochloric acid for about three days, that lost by evaporation 
being replaced, it first swelled up to a soft sponge, gradually assumed 
a caoutchouc-like state, and finally hardened into a dark inadhesive 
mass. The substance, being cut into small pieces, was boiled with 
water, filtered, and dried over a water-bath till the last trace of 
hydrochloric acid retained in the pores of the substance was expelled. 
On cohobation with alcohol a small quantity of the substance dis- 
solved, and this, when examined, showed the usual characteristics of 
unchanged urushic acid. The residue dried at 105° C., gave this 
result on analysis : — 
Carbon, . 
Hydrogen, 
Oxygen, . 
Found. 
77-07 
8-77 
14-16 
100-00 
Mean obtained 
for Urushic Acid. 
77-05 
9*01 
13-94 
100-00 
It appears from this that urushic acid suffers molecular transfor- 
mation (polymerisation) under the influence of strong hydrochloric 
acid. (3 - urushic acid thus formed is a dark brownish solid body, with 
a faint peculiar odour, and soluble with difficulty in the usual 
