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

| Comparative Yield  |  Amount of      |
Substance.     | of Furfuraldehyde. |Glucose Produced.|
---------------+--------------------+-----------------+
Cane sugar     |     1.00           |      ..         |
Starch         |     0.50           |      ..         |
Gum arabic     |     1.33           |    34.72        |
Gum arabic     |     1.20           |    43.65        |
Ghatti, 1      |     1.00           |    26.78        |
Ghatti, 2      |     1.33           |    22.86        |
Metarabin      |     1.75           |      ..         |
---------------+--------------------+-----------------+
>
The amount of reducing sugar calculated as glucose
is also appended.  This was estimated in the residue
left in the flask after distillation by Fehling’s
solution in the usual way.  The yields of furfuraldehyde
would appear to have no definite relation to the other
chemical data about a gum, such as the potash and
baryta absorptions or the sugar produced on inversion.
The action of gum solutions upon polarized light is
interesting, especially in view of the fact that arabin
is itself strongly laevo-rotatory [alpha]_{D} = -99
deg., while certain gums are distinctly dextro-rotatory. 
Hence it is evident that some other body besides arabin
is present in the gum.  We have determined the
rotatory power of a number of gum solutions, the results
of which are subjoined.  On first commencing the
experiments we experienced great difficulty from the
nature of the solutions.  Most of them are distinctly
yellow in color and almost opaque to light, even in
dilute solutions such as 5 percent.  We found
it necessary first to bleach the gums by a special
process; 5 grammes of gum are dissolved in about 40
c.c. of lukewarm water, then a drop of potassium permanganate
is added, and the solution is heated on a water bath
with constant stirring until the permanganate is decomposed
and the solution becomes brown.  A drop of sodium
hydrogen sulphate is now added to destroy excess of
permanganate.  At the same time the solution becomes
perfectly colorless.
It can now be cooled down and made up to 100 c.c.,
yielding a 5 per cent. solution of which the rotatory
power can be taken with ease.  Using a 20 mm.
tube and white light the above numbers were obtained.
----------------+----------------+-----------------
Gum or Dextrin. | Solution used. |    [alpha]_{D}
----------------+----------------+-----------------
|   Per Cent.    |
Aden, 1         |       5        |     — 33.8
Cape, 2         |       5        |     + 28.6
Indian, 3       |       5        |     + 66.2
Eastern, 4      |       5        |     — 26.0
Eastern, 5      |       5        |     — 30.6
Senegal, 6      |       5        |     — 17.6
Senegal, 7      |       5        |     — 18.4
Senegal, 8      |       21/2       |     — 19.6
Senegal, 9      |       5        |     — 38.2
Senegal, 10     |       5        |     — 25.8