The Ghattis are especially good in withstanding climatic changes.

Dextrins containing much starch are less hygroscopic than those which are nearly free from it, as the same conditions which promote the complete conversion of the starch into dextrin also favor the production of sugars, and it is to these sugars probably that commercial dextrin owes its hygroscopic nature. We have been in part able to confirm these results by a series of tests of the same gums in India, but have not yet obtained information as to their behavior in the early part of the year.

The fermentation of natural gum solutions is accompanied by a decrease in the viscosity of the liquid and the separation of a portion of the gum in lumps. Apparently those gums which contain most sugar, as indicated by their reduction of Fehling's solution, are the most susceptible to this change. Oxalic acid is formed by the fermentation, which by combination with the lime present renders the fermenting liquid turbid, and also some volatile acid, probably acetic.

We have made some experiments with a gum which readily fermented--in a week--as to the respective value of various antiseptics in retarding the fermentation. Portions of the gum solutions were mixed with small quantities of menthol, thymol, salol, and saccharin in alkaline solution, also with boric acid, sodium phosphate, and potash alum in aqueous solution. Within a week a growth appeared in a portion to which no antiseptic had been added; the others remained clear. After over five months the solutions were again examined, when the following results were observed:

Antiseptics.	Solution after Five Months.
Menthol in KOH	Some growth at bottom, upper layer clear.
Thymol in KOH	Growth at top, gum white and opaque.
Salol in KOH	Growth at top, gum black and opaque
Saccharin in KOH	White growth at top.
Boric acid	Remained clear; did not smell.
Sodium phosphate	Slight growth at top.
Potash alum	Slight growth at top.

The solution to which no antiseptic had been added was of course quite putrid, and gave the reactions for acetic acid.

In the earlier part of this paper we have given a short account of the chief characteristics of the more important gum substitutes. The following additional notes may be of interest.

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, 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. Per Cent.	BaO absorbed. 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.

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, etc.	Ash.	Acidity. c.c.
1	8.92	81.57	1.99	10.12	None	0.207	57.3
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

In those cases in which the substitute is made by admixture with gelatin or liquid glue the quantity of other organic matter obtained can be checked by a Kjeldahl determination of the total nitrogen. If a natural gum is added, it will be partially converted into sugar when the filtered liquid is inverted, and so make the dextrin determination slightly too high.

[1]A paper read before the Society of Chemical Industry, London, 1891. From the Journal