368 
MR. JOHNSTON ON THE CONSTITUTION OF THE RESINS. 
self for an error of hydrogen in excess. Thus 
Hesse’s formula C 40 H 33 (>! gives 
Carbon 85*66 
Hydrogen 11*53 
Oxygen 2*81 
100 
while C 40 H 34 Oi gives 
85*36 
11*85 
2*79 
100 
The quantity of hydrogen, 1 1*85, in the second column is greater than the minimum 
of water either in Rose’s analyses or mine, and therefore according to the principle 
adopted in deducing all the formulae exhibited in the present series of papers, C 40 H 3 ^ 
0 4 is that which these analyses indicate as the most probable. It is chiefly, I believe, 
to the hygrometric state of the oxide of copper, that analyses performed according to 
the method of Liebig and with equal care, differ slightly in the amount of hydrogen. 
If the oxide be newly prepared by calcining the nitrate, and be therefore in a minute 
state of division, it appears almost impossible, as a general result, to free it so com- 
pletely from moisture that the hydrogen shall not be 0*2 to 0*3 per cent, in excess, 
while the same experimenter will come within 0*1 or 0*1 5 per cent, by the use of oxide 
of copper, which has been frequently heated to redness, and after having been used 
for analysis, has been repeatedly re-oxidized by heating in a current of air. 
XXI. Resin of Bdellium. 
The resin of bdellium occurs in commerce, in translucent yellow rounded masses, 
often of considerable size. The masses vary in tint, as is the case with many other 
resins, some of them being of a brown colour, more or less dark. 
A single yellow mass, about half an inch in diameter, was reduced to powder and 
digested in cold alcohol. A pale yellow solution was obtained, from which, by evapo- 
ration in a thin film, a yellow resin was obtained. It was treated with successive 
portions of boiling distilled water, of which only the first portion acquired a slightly 
yellow tinge. By this treatment it scarcely lost its transparency, differing in this re- 
spect very much from the soluble resins of euphorbium and elemi above-described. 
The resin was then dried for forty-eight hours at 180° Fahr. in the state of a thin 
film. It now formed a beautiful transparent yellow resin, softening readily at 212°, 
and at that temperature emitting a slightly fragrant resinous odour. Burned in the 
air it left 0*17 per cent of ash. 
A. 7‘29 grs. (7*277 grs. pure resin) gave C = 20*15, and H = 6*54 grs. 
B. 7‘185 grs. (7*172 grs. pure resin) gave C = 19*77- 
C. Another lump was treated in a similar manner, and the resin similarly dried. 
Of this 
• • • 
7*687 grs. (7’673 grs. pure resin) gave C = 21*13, and H = 6*9 7 grs. 
D. Of the alcoholic solution of the resin from the same lump, another portion was 
