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   |
9{        |      |        |        |   -38.2   |            |           |
\b......|4.9620| 2.3310 | 2.4180 |           |    -19.4   |   -63.4   |
|      |        |        |           |            |           |
a.|3.4900| 0.3925 | 2.7920 |           |   -104.2   |   -76.0   |
Ghatti{   |      |        |        |  -140.8   |            |           |
\b.|3.2450| 0.4605 | 2.8385 |           |   -106.0   |   -72.4   |
|      |        |        |           |            |           |
a.|2.2550| 0.2900 | 1.8078 |           |   -106.04  |   +68.0   |
Ghatti{   |      |        |        |  -147.05  |            |           |
\b.|2.6635| 0.2845 | 2.3360 |           |   -102.04  |   -66.2   |
----------+------+--------+--------+-----------+------------

+-----------+

The hygrometric nature of a gum or dextrin is a point of considerable importance when the material is to be used for adhesive purposes.  The apparatus which we finally adopted after many trials for testing this property consists simply of a tinplate box about 1 ft. square, with two holes of 2 in. diameter bored in opposite sides.  Through these holes is passed a piece of wide glass tubing 18 in. long.  This is fitted with India rubber corks at each end, one single and the other double bored.  Through the double bored cork goes a glass tube to a Woulffe’s bottle containing warm water.  A thermometer is passed into the interior of the tube by the second hole.  The other stopper is connected by glass tubing to a pump, and thus draws warm air laden with moisture through the tube.  Papers gummed with