184 
Proceedings of the Royal Society 
higher hydrocarbons of the terpene series. It absorbs oxygen from 
the air, and forms a resinous mass. It unites readily with bromine, 
and is blackened by concentrated sulphuric acid in the cold. 
II. Examination of the ivater extract , the Gum . — Gum is a normal 
constituent of lacquer juice, and forms from 3 to 8 per cent, of the 
original liquid. Since gum is insoluble in alcohol, it is conveniently 
separated by treating that portion of the original which was 
insoluble in alcohol with boiling water, filtering, and evaporating 
on a water-bath till the weight becomes constant. In this way a 
friable, light-coloured, tasteless and inodorous substance is obtained. 
This is the anhydrous gum. On combustion it gave the following 
numbers : — 05267 grammes of the substance gave 0*7823 grammes 
of carbonic acid (C0 2 ), 0*2834 grammes water (H 2 0), and 0*0267 
grammes ash. Analysis of 
the ash in a separate sample of the 
substance gave the following 
Silica (Si0 2 ), . 
0*48 
Lime (CaO), 
44*77 
Potash (K 2 0), . 
13*68 
Iron oxide, 
trace. 
Alumina (A1 2 0 3 ), 
7*85 
Magnesia (MgO), 
5*79 
Soda (Na 2 0), . 
1*33 
Carbonic acid (C0 2 ), 
26*10 by difference. 
100*00 
If the metals in the ash be 
| replaced by the equivalent amount of 
hydrogen, and the result calculated 
for carbon, hydrogen, and 
oxygen, the result will be — 
Found. 
Arabic acid 
C 12 H 22 O n . 
Carbon, 
42-47 
42*11 
Hydrogen, . 
6*40 
6*43 
Oxygen, 
. 51*13 
51*46 
100*00 
100*00 
The gum, when inverted, 
has the power of reducing Fehling’s 
solution. 0*4747 grammes 
of the substance (ash deducted), after 
inversion with 10 per cent, hydrochloric acid, and precipitated, gave 
0*8114 grammes of cupric 
oxide. If 
we suppose that after the 
hydration, one molecule of arabic acid (C 12 H 22 O u ) changes into two 
