Scientific American Supplement, No. 821, September 26, 1891

Chapter 11

Chapter 113,291 wordsPublic domain

The yield of furfuraldehyde by the breaking down of arabin and metarabin was thought possibly to be of some value in differentiating the natural gums from one another, but we have not succeeded in obtaining results of much value. 0.2 gramme of a gum were heated with 100 c.c. of 15 per cent. sulphuric acid for about 2½ hours in an Erlenmeyer flask with a reflux condenser. After this period of time, further treating did not increase the amount of furfuraldehyde produced. The acid liquid, which was generally yellow in color, was then cooled and neutralized with strong caustic soda. The neutral or very faintly alkaline solution was then distilled almost to dryness, when practically the whole of the furfuraldehyde comes over. The color produced by the gum distillate with aniline acetate can now be compared with that obtained from some standard substance treated similarly. The body we have taken as a standard is the distillate from the same weight of cane sugar. The tint obtained with the standard was then compared with that yielded by the gum distillate from which the respective ratios of furfuraldehyde are obtained. The following table shows some of these results:

+--------------------+-----------------+ | 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 lævo-rotatory [alpha]_{D} = -99°, 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 | 2½ | - 19.6 Senegal, 9 | 5 | - 38.2 Senegal, 10 | 5 | - 25.8 Amrad | 2½ | + 57.6 Australian, 1 | 5 | - 28.2 Australian, 2 | 5 | - 26.4 Brazilian, 1 | 2½ | - 36.8 Brazilian, 2 | 2½ | + 21.0 Dextrin, 1 | 5 | +148.0 Dextrin, 2 | 5 | +133.2 Ghatti, 1 | 5 | - 39.2 Ghatti, 2 | 5 | - 80.4 ----------------+----------------+-----------------

These numbers do not show any marked connection between the viscosity, etc., of a gum and its specific rotatory power.

When gum arabic solution is treated with alcohol the gum is precipitated entirely if a large excess of spirit be used. With a view to seeing if the precipitate yielded by the partial precipitation of a gum solution was identical in properties to the original gum, we examined several such precipitates from various gums to ascertain their rotatory power. We found in each case that the specific rotatory power of the alcohol precipitate redissolved in water was not the same as that of the original gum. In other words these gums contained at least two bodies of different rotatory powers, of which one is more soluble in alcohol than the other. O'Sullivan obtained similar results with pure arabin. The experiments were conducted in the following manner:

(a.) Five grammes of a dextro-rotatory gum (No. 3 in table) were dissolved in 20 c.c. of water. To the solution was added 90 c.c. of 95 per cent. alcohol. The white precipitate which formed was thrown on to a tared filter and washed with 30 c.c. more alcohol. The total filtrate therefore was 140 c.c. The precipitate was dried and weighed = 2.794 grammes or 55.88 per cent. of the total gum. The precipitate was then redissolved in water, bleached as before and diluted to a 5 per cent. solution. This was then examined in the polarimeter. Readings gave the value [alpha]_{D} = +58.4°. The previous rotatory power of the gum was +66°. Now the alcohol was driven off from the filtrate, which, allowing for the 11.95 per cent. of water in the gum, should contain 32.17 per cent. of gum. The alcohol-free liquid was then diluted to a known volume (for 5 per cent, solution), and [alpha]_{J} found to be +57.7°. This experiment was then repeated again, using 5 grammes of No. 3, when 3.5805 grammes of precipitate were obtained, using the same volumes of alcohol and water. The precipitate gave [alpha]_{J} = +57.4°; the filtrate treated as before, only the percentage of gum dissolved being directly determined instead of being calculated by difference, gave [alpha]_{J} = +52.5°.

(b.) Another gum (No. 9) with [alpha]_{J} = -38.2° and containing 13.86 per cent, of moisture, gave 2.3315 grms. of precipitate when similarly treated. The precipitate gave when redissolved in water [alpha]_{J} = -20.8°. The filtrate containing 39.5 per cent, real gum gave [alpha]_{J} = -67.5°, so that the least lævo-rotatory gum. was precipitated by the alcohol.

The Ghattis apparently are all lævo-rotatory, and give much less alcoholic precipitates than the gum arabic. The precipitation moreover was in the opposite direction, that is, the most lævo-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 the gums or dextrins, etc., to be tested are placed in the tube and the warm moist air passed over them for varying periods, and their proneness to become sticky noted from time to time. By this means the gums can be classified in the order in which they succumbed to the combined influences of heat and moisture. We find that in resisting such influences any natural gum is better than a dextrin or a gum substitute containing dextrin or gelatin. 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:

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 | 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.

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, | Ash. |Acidity. | | | | | &c. | | ----+---------+---------+--------+----------+-------+-------+--------- | | | | | | | cc. 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.

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MR. CAILLETET'S CRYOGEN.

The "cryogen," a new apparatus constructed by Mr. E. Ducretet, from instructions given by Mr. Cailletet, is designed for effecting a fall of temperature of from 70° to 80° C. below zero, through the expansion of liquid carbonic acid.

The apparatus consists of two concentric vessels having an annular space between them of a few centimeters. A worm, S, is placed in the internal vessel R. All this is of nickel plated copper. The worm, S carries, at Ro', an expansion cock and ends, at O in the annular space, R'. A very strong tube is fixed to the cock, Ro', and to the ajutage, A'. It receives the tube, Tu, which, at the time of an experiment, is coupled with the cylinder of carbonic acid, CO². A tubulure, D, usually closed by a plug, Bo, communicates with the inner receptacle, R. This is capable of serving in certain experiments in condensation. The table, Ta, of the tripod receives the various vessels or bottles for the condensed products.

The entire apparatus is placed in a box, B, lined with silk waste and provided with a cover, C, of the same structure. Apertures, Th, Ro, and T", allow of the passage of a key for acting upon the cock, Ro', as well as of thermometers and stirrers if they are necessary.

When it is desired to operate, the internal vessel, R, is filled with alcohol (3 quarts for the ordinary model). This serves as a refrigerant bath for the experiments to be made. The worm, S, having been put in communication with the carbonic acid cylinder, CO², the cock, Ro, of the latter is turned full on. The cock of the worm, which is closed, is opened slightly. The vaporization and expansion of the liquid carbonic acid cause it to congeal in the form of snow, which distributes itself and circulates in the worm, S, and then in R. The flakes thus coming in contact with the metallic sides of S rapidly return to the gaseous state and produce an energetic refrigeration. At the lower part of the annular space, R', are placed fragments of sponge impregnated with alcohol. The snow that has traversed the worm without vaporizing reaches R'. and dissolves in this alcohol, and the refrigeration that results therefrom completes the lowering of the temperature. The gas finally escapes at O, and then through the bent tube, T".

The apparatus may be constructed with an inverse circulation, the carbonic acid then entering the annular vessel, R, directly, and afterward the worm, S, whence it escapes to the exterior of the apparatus. The expansion cock sometimes becomes obstructed by the solidification of the snow. It will then suffice to wait until the circulation becomes re-established of itself. It may be brought about by giving the cock, Ro', a few turns with the wooden handled key that serves to maneuver the latter. It is not necessary to have a large discharge of carbonic acid, and consequently the expansion cock needs to be opened but a little bit. A few minutes suffice to reduce the temperature of the alcohol bath to 70°, with an output of about from 4½ to 5½ lb. of liquid carbonic acid. When the circulation is arrested, the apparatus thus surrounded by its isolating protective jackets becomes heated again with extreme slowness. In one experiment, it was observed that at the end of nine hours the temperature of the alcohol had risen but from 70° to 22°. On injecting a very small quantity of liquid carbonic acid from time to time, a sensibly constant and extremely low temperature may be maintained indefinitely.--_Le Genie Civil_.

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METHOD OF PRODUCING ALCOHOL.