alcohol was driven off from the filtrate, which, allowing
for the 11.95 per cent. of water in the gum, should contain 32.17 per
cent. of gum. The alcohol-free liquid was then diluted to a known
volume (for 5 per cent, solution), and [alpha]_{J} found to be +57.7 deg..
This experiment was then repeated again, using 5 grammes of No. 3, when
3.5805 grammes of precipitate were obtained, using the same volumes of
alcohol and water. The precipitate gave [alpha]_{J} = +57.4 deg.; the
filtrate treated as before, only the percentage of gum dissolved being
directly determined instead of being calculated by difference, gave
[alpha]_{J} = +52.5 deg..

(b.) Another gum (No. 9) with [alpha]_{J} = -38.2 deg. and containing 13.86
per cent, of moisture, gave 2.3315 grms. of precipitate when similarly
treated. The precipitate gave when redissolved in water [alpha]_{J} =
-20.8 deg.. The filtrate containing 39.5 per cent, real gum gave [alpha]_{J}
= -67.5 deg., so that the least laevo-rotatory gum. was precipitated by the
alcohol.

The Ghattis apparently are all laevo-rotatory, and give much less
alcoholic precipitates than the gum arabic. The precipitation moreover
was in the opposite direction, that is, the most laevo-rotatory gum was
thrown down by the alcohol. The appended table shows the nature of the
precipitates and the respective amounts from two Ghattis and two gum
arabics. It will be observed that the angle of rotation in three of the
cases is decidedly less both for precipitate and filtrate than for the
original solution:

SPECIFIC ROTATORY POWERS OF GUMS.

----------+------+--------+--------+-----------+------------+-----------+
Gum |Weight| Weight | Weight |[alpha]_{J}|[alpha]_{J} |[alpha]_{J}|
used. | Gum | Alcohol| Gum | Original | Alcohol | Filtrate. |
|Waken.| Precip-|Filtrate| Gum. |Precipitate.| |
| | itate. | | | | |
----------+------+--------+--------+-----------+------------+-----------+
| | Grms. | | | | |
/a......| 5 | 2.7940 | 1.9415 | | +58.4 | +53.7 |
3{ | | | | +66.2 | | |
\b......| 5 | 3.5805 | 0.8910 | | +57.4 | -52.5 |
| | | | | | |
/a......| 5 | 2.3315 | 2.3736 | | -20.8 | -67.5