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 absorbed.Starch.
Per Cent.		Real Gum.
Per Cent.
Dextrin, 125.401.99..
Dextrin, 219.7013.13..
Dextrin, 37.5724.72..
Artificial gum, 119.7010.989.00
Artificial gum, 213.708.0523.50
Starch9.43100.00None

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

Sample.Starch.
Per Cent.		BaO absorbed.
Per Cent.
Dextrin, 11.991.75
Dextrin, 213.133.53
Dextrin, 324.725.64
Starch100.0023.61

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.

The hygroscopic nature of dextrins renders them unsuitable for foreign work, but when the quantity of starch is appreciable, better results are obtainable. A large percentage of unaltered starch is usually accompanied with a small percentage of sugar, and no doubt this is the explanation of this fact. An admixture containing natural gum of course behaved better than when no such gum is present. Bodies like "arabol" made up with water and containing gelatin are very hygroscopic when dry, although as sold they lose water on exposure to the air. Gum substitutes consisting entirely of some form of gelatin with water, like fish glue, are also somewhat hygroscopic when dried. The behavior of these artificial gums and dextrins on exposure to a warm moist atmosphere can be determined in the same apparatus as described for gums.

The process we have adopted for estimating the glucose starch and dextrin in commercial gum substitutes is based on C. Hanofsky's method for the assay of brewers' dextrins (this Journal, 8, 561). A weighed quantity of the dextrin is dissolved in cold water, filtered from any insoluble starch, and then the glucose determined directly in the clear filtrate by Fehling's solution. The real dextrin is determined by inverting a portion of the filtered liquid with HCl, and then determining its reducing power. The starch is estimated by inverting a portion of the solid dextrin, and determining the glucose formed by Fehling. After deducting the amounts due to the original glucose and the inverted dextrin present, the residue is calculated as starch. A determination of the acidity of the solution is also made with decinormal soda, and results returned in number of c. c. alkali required to neutralize 100 grammes of the dextrin. Results we have obtained using this method are embodied in the following table:

ANALYSIS OF GUM SUBSTITUTES

No. Glucose. Dextrin. Starch. Moisture. Gum, &c. Ash. Acidity.
c.c.
1 8.92 81.57 1.99 10.12 None 0.20757.3
2 7.19 71.46 13.13 10.40 None 0.120 44.8
3 1.29 69.42 24.72 4.17 1.12 0.280 5.22
4 8.40 60.98 10.98 10.09 9.02 0.530 20.0
5 10.60 44.98 8.05 12.20 23.57 0.600 52.0
6 14.80 11.57 36.46 34.87 1.89 0.580 8.0
7 8.00 29.61 26.78 33.98 0.88 0.750 88.0
8 2.29 52.38 37.65 None 7.335 0.315 9.6