The ashes of most gum substitutes, consisting chiefly of dextrin, are characterized by the high percentage of chlorides they contain, due no doubt to the use of hydrochloric acid in their preparation.  The soluble constituents of the ash consist of neutral alkaline salts, but as a rule no alkaline carbonates, and it is thus possible to demonstrate the absence of any natural gum in such a compound.  We have seldom noticed the presence of any sulphates in such ashes, but when sulphurous or sulphuric acids have been used in the starch conversion it will be found in small quantities.

We have already pointed out that the potash absorption value of a gum is low and that dextrins give high numbers, but the latter vary very considerably, and as the starch and sugar present also influence the potash absorption value, it does not give information of much service.  The following table shows the kind of results obtained: 

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

+--------------
Sample.            |   KOH    |   Starch.    | Real Gum.
| absorbed.|              |
-----------------------------+----------+--------------+----

----------
|          |  Per Cent.   | Per Cent. 
Dextrin, 1                   |  25.40   |     1.99     |    .. 
Dextrin, 2                   |  19.70   |    13.13     |    .. 
Dextrin, 3                   |   7.57   |    24.72     |    .. 
Artificial gum, 1            |  19.70   |    10.98     |   9.00
Artificial gum, 2            |  13.70   |     8.05     |  23.50
Starch                       |   9.43   |   100.00     |   None
-----------------------------+----------+--------------+----

----------

The baryta absorptions seem to be chiefly due to the quantity of starch present in the composition: 

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

---------------
Sample.          |    Starch.    |       BaO
|               |      absorbed.
----------------------------+---------------|---------------

----------
|   Per Cent.   |      Per Cent. 
Dextrin, 1                  |      1.99     |        1.75
Dextrin, 2                  |     13.13     |        3.53
Dextrin, 3                  |     24.72     |        5.64
Starch                      |    100.00     |       23.61
----------------------------+---------------+---------------

----------

The viscosity of a dextrin or artificial gum is determined in exactly the same way as a natural gum, using 10 per cent. solutions.  It would probably be an improvement to use 10 per cent. solutions for many of the dextrins, as they are when low in starch extremely thin.