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

Chapter V: Part 5

Text size

can be obtained, and thus the value of Z_{t°} for any required temperature. The numbers calculated for gums all point to a diminution in viscosity up to a certain point, and then a gradual increase. A comparison of some of the figures actually obtained in some of these experiments, compared with the calculated figures for the same temperature, shows their general agreement.

EFFECT OF TEMPERATURE UPON VISCOSITY--GUM VII.

------------+------+--------+-------------+
Temperature.| [eta]|Z found.|Z calculated.|
------------+------+--------+-------------+
°C | | | |
50 |0.0283| 228 | 228.00 |
45 |0.0305| 246 | 246.55 |
42 |0.0352| 284 | 266.75 |
38 |0.0368| 297 | 289.00 |
34 |0.0410| 330 | 313.06 |
30 |0.0419| 339 | 339.00 |
26 |0.0445| 359 | 367.80 |
22 |0.0492| 398 | 396.47 |
20 |0.0511| 412 | 412.00 |
18 |0.0531| 428 | 428.00 |
------------+------+--------+-------------+

EFFECT OF TEMPERATURE UPON VISCOSITY.--GUM VIII.

------------+------+--------+-------------|
Temperature.| [eta]|Z found.|Z calculated.|
------------+------+--------+-------------|
°C. | | | |
50 |0.0430| 347 | 347 |
46 |0.0475| 383 | 371.14 |
42 |0.0502| 405 | 397.09 |
38 |0.0510| 411 | 424.73 |
34 |0.0575| 463 | 454.06 |
30 |0.0602| 485 | 485 |
26 |0.0637| 513 | 517.82 |
22 |0.0667| 538 | 552.25 |
20 |0.0707| 570 | 570 |
18 |0.0755| 609 | 583.07 |
------------+------+--------+-------------+

The constants for the first gum are those given in the preceding column, while for the latter they were--

A = 771.9: B = -11.15: C = 0.053

As will be observed, the effect of heat appears to be the same upon the two typical gum arabics quoted above, an increase of temperature from 18° C. to 50° C. decreasing the viscosity by nearly one half in both cases, and the same seems to be true of most gum arabics. Roughly also the same holds good for Ghattis, as the following numbers show:

------------+-------------+------------|
Gum. | Z at 18° C. | Z at 50° C.|
------------+-------------+------------|
Gum arabic. | 1016 | 579 |
Gum arabic. | 428 | 228 |
Gum arabic. | 609 | 347 |
Gum arabic. | 581 | 258 |
Ghatti. | 572 | 306 |
Ghatti. | 782 | 418 |
---------------------------------------+

The following table shows the effect of heat upon the viscosity of a typical Ghatti:

GHATTI GUM NO. 15.--VISCOSITY.

------------+------+-----|
Temperature.| [eta]| Z. |
------------+------+-----|
°C. | | |
50 |0.0517| 418 |
46 |0.0581| 468 |
42 |0.0628| 506 |
38 |0.0726| 585 |
34 |0.0788| 635 |
30 |0.0857| 691 |
26 |0.0889| 717 |
22 |0.0919| 741 |
20 |0.0946| 763 |
18 |0.0964| 777 |
------------+------+-----+

There is therefore no essential difference in the behavior of a Ghatti and a gum arabic on heating. Some interesting results, however, were obtained by heating gums, both Ghattis and arabics, at a fixed temperature for the same time, cooling, and then after making the solutions up to the original volume taking their viscosities at the ordinary temperature. The effect of heating for two hours to 60° C., 80° C., or 100° C. was a small permanent alteration in viscosity of the solution, and it would therefore seem desirable that gum solutions should be made up cold to get the maximum results. The following numbers illustrate this change, viz.:

------------------------+-----------+-----------------------+ | | After heating to | Gum Arabic | Without |-------+-------+-------+ 10 Per Cent. | heat. | 60°C. | 80°C. | 100°C | ------------------------+-----------+-------+-------+-------+ Z at 18°C | 570 | 468 | 470 | 517 | Z at 30°C | 485 | 400 | 422 | 439 | Z at 50°C | 347 | 287 | 258 | 301 | Ghatti gum No. 15, | | | | | 5 per cent. Z at 18°C. | 1,104 | 780 | 660 | 758 | ------------------------+-----------+-------+-------+-------+

The variation of viscosity with strength of solution was also studied with one or two typical gums. A 10 per cent. is invariably more than twice as viscous as a 5 per cent. solution. The following curve was obtained from one of the Ghattis. Similar results were shown by other gums.

It would seem, therefore, that strong solutions, say of 50 per cent. strength, would be more alike in viscosity than solutions of 5 per cent. strength of the same gums. In other words, the viscosity of a gum solution should be taken as nearly as possible to the strength it is used at, to obtain an exact quantitative idea of its gumming value.

The observation of this fact was one of the circumstances which decided us to use 5 per cent. solutions for the determination of Ghatti gum viscosities, the ratio between the 5 per cent. and 10 per cent. solutions of gum arabics being roughly the same as that between the respective weights required for gumming solutions of equal value.

From observation of the general nature of the solutions of Ghatti gums, and from the fact that when allowed to stand portions of the apparently insoluble matter passed into solution, the hypothesis suggested itself that metarabin was soluble in arabin, although insoluble in cold water. If this hypothesis were correct, it would explain the apparent anomaly of Ghattis giving solutions of higher viscosity than gum arabics, although they leave insoluble matter behind. The increase in viscosity would be due to the thickening of the arabic acid by the metarabin. Moreover, the solutions yielded by various Ghattis leaving insoluble matter behind would _be all of the same kind_, viz., a saturated solution of metarabin in arabin more or less diluted by water. Still further, if the insoluble residue of a Ghatti be the residual metarabin over and above that required to saturate the arabin, then it will be possible to dissolve this by the addition of more arabin in the form of ordinary gum arabic. In order to see if this were the case the following experiments were performed. Equal parts of a Ghatti and of a gum arabic were ground up together and dissolved in water. The resulting solution was _clear_. It was diluted until of 10 per cent. strength, and its viscosity then taken:

---------------------+-------------+----------------+ | Contains 50 per Cent. Ghatti.| ---------------------+-------------+----------------+ A. Pressure 200 mm | [eta] | Z. | Temperature 15° C | 0.2517 | 2,030 | ---------------------+-------------+----------------+

The viscosity of this solution therefore was considerably greater than the mean viscosity of the 10 per cent. solutions of the Ghatti and the gum arabic, viz., (0.288 + 0.0636)/2 = 0.1758 for the calculated [eta]. Hence it is evident that the increase in viscosity is due to the solution of the metarabin.

Next a solution was made from a mixture of 70 per cent. Ghatti and 30 per cent. gum arabic. This was also clear and gave a considerably higher viscosity than the previous solution.

---------------------+------------------------------+ | Contains 70 per Cent. Ghatti.| ---------------------+-------------+----------------+ B. Pressure 200 mm | [eta] | Z. | Temperature 15° C | 0.3177 | 2,562 | ---------------------+-------------+----------------+

It will be obvious that the increase of viscosity over the previous solution in this case must be due to the smaller amount of the thin gum arabic which is present, _i.e._, in the first case there is more gum arabic than is required to dissolve the whole of the insoluble metarabin. Further experiments showed that this is also true of the second mixture, as the viscosities of the following mixtures illustrate:

-------------------------+--------+-------+
Strength of Solution. | [eta] | Z. |
-------------------------+--------+-------|
C. 80 per cent. Ghatti. |0.3642 | 2,937 |
D. 75 per cent. Ghatti. |0.33095 | 2,669 |
E. 77.5 per cent. Ghatti.|0.4860 | 3,819 |
-------------------------+--------+-------+

This last solution E we called for convenience the "maximum viscosity" solution, as we believe it to be a 10 per cent. solution containing arabin very nearly saturated with metarabin. As will be observed, its viscosity differs widely from those of solutions C and D, between which it lies in percentage of Ghatti. The first named solution C contains _too little_ of gum arabic to dissolve the whole of the metarabin. Consequently there is a residue left undissolved, which of course diminishes its viscosity. The second solution D is too low in viscosity, as it still contains too much of the weak gum arabic, and as will be seen further on, a very slight change in the proportions increases or decreases the viscosity enormously.

We next tried a series of similar experiments with a Ghatti containing far less insoluble residue and which consequently would require less gum arabic to produce a perfect solution. Mixtures were made in the following proportions, viz.:

----------------------+------------+-----------+
----- | 13.3 per Cent. Ghatti. |
----------------------+------------+-----------+
F. Pressure 200 mm. | [eta] | Z. |
Temperature 15° C. | 0.0976 | 787 |
----------------------+------------+-----------+

----------------------+------------+-----------+
----- | 86.6 per Cent. Ghatti. |
----------------------+------------+-----------+
G. Pressure 200 mm. | [eta] | Z. |
Temperature 15° C. | 0.4336 | 3,497 |
----------------------+------------+-----------+

This latter solution is approaching fairly closely to our "maximum viscosity" with the previous Ghatti, and probably a very slight decrease in the amount of gum arabic would bring about the required increase in viscosity.

When these experiments were first commenced we were still under the impression, which several months' experience of working with gums had produced, namely, that the Ghattis were quite distinct in their properties to ordinary gum arabics. But the new hypothesis, and the experiments undertaken to confirm it, showed clearly that if the viscosity of a gum solution depends on the ratio of metarabin to arabin, then there is no absolute line of demarkation between a Ghatti and a gum arabic. In other words, there is a constant gradation between gum arabic and Ghattis, down to such gums as cherry gum, consisting wholly of metarabin and quite insoluble in water. Therefore those gum arabics which are low in viscosity consist of nearly pure arabin, while as the viscosity increases so does the amount of metarabin, until we come to Ghattis which contain more metarabin than their arabin can hold in solution, when their viscosity goes down again.

From these observations it would follow, that by taking a gum of less viscosity than the gum arabic previously used to dissolve the Ghatti, less of it would be required to do the same work. We confirmed this suggestion experimentally by taking another gum arabic of viscosity 0.0557 at 15° C. A mixture containing 93.3 per cent. of this Ghatti and 6.7 per cent. of our thinnest gum arabic gave a clear solution which had the highest viscocity we have yet obtained for a 10 per cent. solution.

----------------------+--------+-------+
H. Pressure 200 mm. | [eta] | Z. |
Temperature 15° C. | 0.5525 | 4,456 |
----------------------+--------+-------+

This gum arabic may be regarded as nearly pure arabin (as calcium and potassium, etc., salt). By diluting the new "maximum viscosity" solution, therefore, with the 10 per cent. solution of the gum arabic in fixed proportions we obtain a series of viscosities which are shown in the following curve.

Besides obtaining this curve for change in viscosity from maximum amount of metarabin to no metarabin at all, we also traced the decrease in viscosity of the "maximum" solution by dilution with water. The following numbers were thus obtained, and plotted out into a curve.

Having obtained this curve, we are now in a position to follow up the hypothesis by calculating the surplus amount of insoluble matter in a Ghatti. For, let it be conceded that the solution of any Ghatti leaving an insoluble residue is a mixture of arabin and metarabin in the same ratio as our "maximum" solution, only more diluted with water, then from the found viscosity we obtain a point on the curve for dilution, which gives the percentage of dissolved matter.

Now to show the use of this: The Z value for a 10 per cent. solution of the second Ghatti at 15° C. is 2,940. This corresponds on the curve to 8.4 dissolved matter. 10 - 8.4 = 1.6 grammes in 10 grammes, which is insoluble.

CHANGE OF VISCOSITY WITH DILUTION--"MAXIMUM" SOLUTION. 15° C. TEMPERATURE.

------------+--------------+---------
Percentage. | [eta] | Z.
------------+--------------+---------
10 | 0.55250 | 4,456
9 | 0.42850 | 3,456
8 | 0.35120 | 2,832
7 | 0.27660 | 2,230
6 | 0.22290 | 1,797
5 | 0.16810 | 1,355
4 | 0.11842 | 955
3 | 0.08020 | 647
2 | 0.06190 | 499
1 | 0.03610 | 291
------------+--------------+---------

We have already shown that a "maximum" viscosity solution of this gum is formed when 6.7 per cent, of thin gum arabic is added to it, and therefore 6.7 parts of a thin gum arabic are required to bring 16 parts of metarabin into solution. A convenient rule, therefore, in order to obtain complete solution of a Ghatti gum is to add half the weight in thin gum of the insoluble metarabin found from the viscosity determination. But the portion of the gum which dissolved is made up in a similar manner (being a diluted "maximum" solution).

Therefore the 84 per cent. of soluble matter contains 58 parts of metarabin, and the total metarabin in this gum is 58 + 16 = 74 per cent, on the dry gum.

With these solutions of high viscosity some other work was done which may be of interest. The temperature curves of the mixtures marked E, G, and F were obtained between 60° C. and 15° C. The two former curves showed a direction practically parallel to that at the 10 per cent. solutions, and as they were approaching to the "maximum" solution, this is what one would expect. Mr. S. Skinner, of Cambridge, was also good enough to determine the electrical resistances of these solutions and the Ghattis and gum arabics employed in their preparation. The electrical resistance of these gum solutions steadily diminishes as the temperature increases, and the curve is similar to those obtained for rate of change with temperature. Although the curves run in, roughly, the same direction, there does not appear to be any exact ratio between the viscosities of two gums say at 15° C. and their electrical resistances at the same temperature; hence it would not seem possible to substitute a determination of the electrical resistance for the viscosity determination. The results appear to be greatly influenced by the amount of mineral matter present, gums with the greatest ash giving lower resistances.

Experiments were conducted with two Ghattis and two gum arabics, besides the mixtures marked E, F, and H. Comparison of the electrical resistances with the viscosities at 15° C. shows the absence of any fixed ratio between them.

-----------+------+-------------+------------
Gum or | °C. | Ohms | Z Viscosity
Mixture. | | Resistance. | at 15° C.
-----------+------+-------------+-------------
Ghatti, 1 | 10 | 5,667 | 1,490
Ghatti, 2 | 15 | 2,220 | 2,940
Arabic 1 | 15 | 1,350 | 605
Arabic 2 | 10 | 2,021 | 449
Mixture F | 15 | 1,930 | 787
Mixture E | 11.3 | 2,058 | 3,919
-----------+------+-------------+-------------

While performing these experiments, an attempt was made to obtain an "ash-free" gum, in order to compare its viscosity with that of the same gum in its natural state. A gum low in ash was dissolved in water, and the solution poured on to a dialyzer, and sufficient hydrochloric acid added to convert the salts into chlorides. When the dialyzed gum solution ceased to contain any trace of chlorides, it was made up to a 10 per cent. solution, and its viscosity determined under 100 mm. pressure, giving the following results at 15° C.:

-----------------+--------------+-----
-------- | [eta] | Z
-----------------+--------------+-----
Natural gum..... | 0.05570 | 449
"Ash-free" gum.. | 0.05431 | 438
-----------------+--------------+-----

Thus showing that the viscosity of pure arabin is almost identical with that of its salts in gum.

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.

* * * * *

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_.

* * * * *

METHOD OF PRODUCING ALCOHOL.

In carrying out my improved process in and with the apparatus employed in ordinary commercial distilleries, says Mr. Alfred Springer, of Cincinnati, O., I preferably employ separate vats or tubs for the nitric acid solution and the material to be treated, and a convenient arrangement is to locate the nitric acid tub directly under the grain tub, so that one may discharge into the other. In the upper vat is placed the farinaceous material, preferably ground, thoroughly steeped in three times its weight of water, and, where whole grain is used, preferably "cooked" in the ordinary manner. The vat into which the dilute acid is placed is an ordinary cooking tub of suitable material to resist the acid, provided with closed steam coils and also nozzles for the discharge of steam into the contained mass. Into this vat is placed for each one hundred parts of the grain to be treated one part of commercial nitric acid diluted with fifty parts of water and brought to a state of ebullition and agitation by the steam coils and the discharge through the nozzles, the latter being regulated so that the gain by condensation of steam approximately equals the loss by evaporation. The farinaceous contents of the upper vat are allowed to flow slowly into the nitric acid solution while the ebullition and agitation of the mass is continued. This condition is then maintained for six to eight hours, after which the mass is allowed to stand for one day or until the saccharification becomes complete. The conversion can be followed by the "iodine test" for intermediary dextrins and the "alcohol test" for dextrin. After the saccharification is complete I may partially or wholly neutralize the nitric acid, preferably with potassium or Ammonium carbonate, preferably employing only one-half the amount necessary to neutralize the original quantity of nitric acid used, so that the mass now ready to undergo fermentation has an acid reaction. The purpose in view here is to keep the peptones in solution also, because an acid medium is best adapted to the propagation of the yeast cells. It is not absolutely necessary to even partially neutralize the nitric acid, but it is preferable. Yeast is now added, and the remaining processes are similar to those generally employed in distilleries, excepting that just prior to distillation potassium carbonate sufficient to neutralize the remaining nitric acid is added, in order to avoid corrosion of the still and correct the acid reaction of the slop.

As a variant of the process I sometimes add to the usual amount of nitric acid an additional one one-hundredth part of phosphoric acid on account of its beneficial nutritive powers--that is to say, to one hundred parts of grain one part of nitric acid and one one-hundredth part of phosphoric acid.

While my improved process is based on the well-known converting power of acids on starch, I am not aware that it has ever been applied in the manner and for the purposes I have described. For example, sulphuric and hydrochloric, also sulphuric and nitric, acids have been employed in the manufacture of glucose; but in every such case the resulting products were not capable of superseding those obtained by the existing methods of saccharification used in distilleries. In my process, on the other hand, the product is so capable. Not only may malted grain be entirely omitted, but more fermentable products are formed and the products of fermentation are purer. The saccharification being more complete, there are less intermediary and nonfermentable dextrins, and the yield of spirits is therefore increased. Malted grain being omitted or used in reduced quantity, there is less lactic acid and few or foreign ferments to contaminate the fermenting mass; also, the formation of higher alcohols than the ethyl alcohol is almost totally suppressed. Consequently the final yield of spirits is purer in quality and requires little or no further purification. Also, further, the nitrates themselves acting as nutrients to the yeast cells, these become more active and require less nutrition to be taken from the grain.

* * * * *

SPECTROSCOPIC DETERMINATION OF THE SENSITIVENESS OF DRY PLATES.

After describing other methods of determining the sensitiveness of plates, Mr. G.F. Williams, in the _Br. Jour. of Photo_., thus explains his plan. I will now explain the method I adopt to ascertain the relative sensitiveness of plates to daylight. Procure a small direct vision pocket spectroscope, having adjustable slit and sliding focus. To the front of any ordinary camera that will extend to sixteen or eighteen inches, fit a temporary front of soft pine half an inch thick, and in the center of this bore neatly with a center bit a hole of such diameter as will take the eye end of the spectroscope; unscrew the eyehole, and push the tube into the hole in wood, bushing the hole, if necessary, with a strip of black velvet glued in to make a tight fit. By fixing the smaller tube in the front of camera we can focus by sliding the outer tube thereon; if we fix the larger tube in the front, we should have to focus inside the camera, obviously most inconvenient in practice. Place the front carrying the spectroscope _in situ_ in the camera, and rack the latter out to its full extent; point the camera toward a bright sky, or the sun itself, if you can, while you endeavor to get a good focus. The spectrum will be seen on the ground glass, probably equal in dimensions to that of a quarter plate. Proceed to focus by sliding the outer tube to and fro until the colors are quite clear and distinct, and at same time screw down the slit until the Fraunhofer lines appear. By using the direct rays of the sun, and focusing carefully, and adjusting the slit to the correct width, the lines can be got fairly sharply. Slide your front so that the spectrum falls on the ground glass in just such a position as a quarter plate glass would occupy when in the dark slide, and arrange matters so that the red comes to your left, and the violet to the right, and invariably adopt that plan. It is advisable to include the double H lines in the violet on the right hand edge of your plate. They afford an unerring point from which you can calculate backward, finding G, F, E, etc., by their relative positions to the violet lines. Otherwise you may be mistaken as to what portion of the spectrum you are really photographing. The red should just be seen along the left edge of the quarter plate. When all is arranged thus, you utilize three-fourths of your plate with the spectrum, with just a little clear glass at each end. Before disturbing the arrangement of the apparatus, it is desirable to scratch a mark on the sliding tube, and make a memorandum of the position of all the parts, so that they may be taken away and replaced exactly and thus save time in future.

To take a photograph of the spectrum, put a quarter plate in the dark slide and place in camera; point the camera toward a bright sky, or white cloud, near the sun--not at the sun, as there is considerable difficulty in keeping the direct rays exactly in the axis of the spectroscope--draw the shutter, and give, say, sixty seconds. On development, you will probably obtain a good spectrum at the first trial. The duration of exposure must, of course, depend upon the brightness of the day; but if the experiments are to have relative values, the period of exposure must be distinctly noted, and comparisons made for a normal exposure of sixty seconds, ninety seconds, two minutes or more, just according to whatever object one has in view in making the experiments. With a given exposure the results will vary with the light and the width of the slit, as well as being influenced by the character of the instrument itself. Further, all such experiments should be made with a normal developer, and development continued for a definite time. The only exception to this rule would be in the event of wishing to ascertain the utmost that could be got out of a plate, but, under ordinary circumstances, the developer ought never to vary, nor yet the duration of development. To try the effect of various developers, or varying time in development, a departure must be made of such a nature as would operate to bring out upon each plate, or piece of a plate, the utmost it would develop short of fog, against which caution must be adopted in all spectrum experiments.

On development, say for one, two, or three minutes, wash off and fix. You will recognize the H violet lines and the others to the left, and this experiment shows what is the sensitiveness of this particular plate to the various regions of the spectrum with this particular apparatus, and with a normal exposure and development. So far, this teaches very little; it merely indicates that this particular plate is sensitive or insensitive to certain rays of colored light. To make this teaching of any value, we must institute comparisons. Accordingly, instead of simply exposing one plate, suppose we cut a strip from two, three, four, or even half a dozen different plates, and arrange them side by side, horizontally, in the dark slide, so that the spectrum falls upon the whole when they are placed in the camera and exposed. There is really no difficulty in cutting strips a quarter of an inch wide, the lengthway of a quarter plate. Lay the gelatine plate film up, and hold a straight edge on it firmly, so that when we use a suitable diamond we can plow through the film and cut a strip which will break off easily between the thumb and finger. A quarter plate can thus be cut up into strips to yield about a dozen comparative experiments. When cut and snapped off, mark each with pencil with such a distinguishing mark as shall be clearly seen after fixing. The cut up strips can be kept in the maker's plate box.

* * * * *

The deep down underground electric railway in London has so far proved an unprofitable concern for its stockholders. It is 3½ miles long, touches some of the greatest points of traffic, but somehow or other people won't patronize it. The total receipts for the last six months were a little under $100,000, and they only carried seventeen persons per train mile. On this road the passengers are carried on elevators up and down from the street level to the cars. The poor results so far make the stockholders sick of the project of extending the road.

* * * * *

A NEW CATALOGUE OF VALUE

Contained in Scientific American Supplement during the past ten years, sent _free of charge_ to any address. Munn & Co., 361 Broadway, New York.

* * * * *

THE SCIENTIFIC AMERICAN

ARCHITECTS AND BUILDERS EDITION

$2.50 a Year. Single Copies, 25 cts.

This is a Special Edition of the Scientific American, issued monthly--on the first day of the month. Each number contains about forty large quarto pages, equal to about two hundred ordinary book pages, forming, practically, a large and splendid Magazine of Architecture, richly adorned with _elegant plates in colors_ and with fine engravings, illustrating the most interesting examples of modern Architectural Construction and allied subjects.

A special feature is the presentation in each number of a variety of the latest and best plans for private residences, city and country, including those of very moderate cost as well as the more expensive. Drawings in perspective and in color are given, together with full Plans, Specifications, Costs, Bills of Estimate, and Sheets of Details.

No other building paper contains so many plans, details, and specifications regularly presented as the Scientific American. Hundreds of dwellings have already been erected on the various plans we have issued during the past year, and many others are in process of construction.

Architects, Builders, and Owners will find this work valuable in furnishing fresh and useful suggestions. All who contemplate building or improving homes, or erecting structures of any kind, have before them in this work an almost _endless series of the latest and best examples_ from which to make selections, thus saving time and money.

Many other subjects, including Sewerage, Piping, Lighting, Warming, Ventilating, Decorating, Laying out of Grounds, etc., are illustrated. An extensive Compendium of Manufacturers' Announcements is also given, in which the most reliable and approved Building Materials, Goods, Machines, Tools, and Appliances are described and illustrated, with addresses of the makers, etc.

The fullness, richness, cheapness, and convenience of this work have won for it the Largest Circulation of any Architectural publication in the world.

A Catalogue of valuable books on Architecture, Building, Carpentry, Masonry, Heating, Warming, Lighting, Ventilation, and all branches of industry pertaining to the art of Building, is supplied free of charge, sent to any address.

MUNN & CO., PUBLISHERS, 361 BROADWAY, NEW YORK.

* * * * *

BUILDING PLANS AND SPECIFICATIONS.

In connection with the publication of the Building; EDITION of the Scientific American, Messrs, Munn; & Co. furnish plans and specifications for buildings' of every kind, including Churches, Schools, Stores, Dwellings, Carriage Houses, Barns, etc.

In this work they are assisted by able and experienced architects. Full plans, details, and specifications for the various buildings illustrated in this paper can be supplied.

Those who contemplate building, or who wish to alter, improve, extend, or add to existing buildings, I whether wings, porches, bay windows, or attic rooms, fare invited to communicate with the undersigned. Our work extends to all parts of the country. Estimates, plans, and drawings promptly prepared. Terms moderate. Address

MUNN & CO., 361 BROADWAY, NEW YORK.

* * * * *

THE SCIENTIFIC AMERICAN SUPPLEMENT.

Published Weekly. Terms of Subscription, $5 a year.

Sent by mail, postage prepaid, to subscribers in any part of the United States or Canada. Six dollars a year, sent, prepaid, to any foreign country.

All the back numbers of The Supplement, from the commencement. January I, 1876, can be had. Price, 10 cents each.

All the back volumes of The Supplement can likewise be supplied. Two volumes are issued yearly. Price of each volume, $2.50 stitched in paper, or $3.50 bound in stiff covers.

Combined Rates.--One copy of Scientific American and one copy of Scientific American Supplement, one year, postpaid, $7.00.

A liberal discount to booksellers, news agents, and canvassers.

MUNN & CO., PUBLISHERS,

361 BROADWAY, NEW YORK, N.Y.

* * * * *

USEFUL ENGINEERING BOOKS

Manufacturers, Agriculturists, Chemists, Engineers, Mechanics, Builders, men of leisure, and professional men, of all classes, need good books in the line of their respective callings. Our post office department permits the transmission of books through the mails at very small cost. A comprehensive catalogue of useful books by different authors, on more than fifty different subjects, has recently been published, for free circulation, at the office of this paper. Subjects classified with names of author. Persons desiring a copy have only to ask for it, and it will be mailed to them. Address,

MUNN & CO., 361 BROADWAY, NEW YORK.

* * * * *

PATENTS!

Messrs. Munn & Co., in connection with the publication of the Scientific American, continue to examine improvements, and to act as Solicitors of Patents for Inventors.

In this line of business they have had _forty-five years experience_, and now have _unequaled facilities_ for the preparation of Patent Drawings, Specifications, and the prosecution of Applications for Patents in the United States, Canada, and Foreign Countries. Messrs. Munn & Co. also attend to the preparation of Caveats, Copyrights for Books, Labels, Reissues, Assignments, and Reports on Infringements of Patents. All business intrusted to them is done with special care and promptness, on very reasonable terms.

A pamphlet sent free of charge, on application, containing full information about Patents and how to procure them; directions concerning Labels, Copyrights, Designs, Patents, Appeals, Reissues, Infringements, Assignments, Rejected Cases. Hints on the Sale of Patents, etc.

We also send, _free of charge_, a Synopsis of Foreign Patent Laws, showing the cost and method of securing patents in all the principal countries of the world.

MUNN & CO., SOLICITORS OF PATENTS, 361 Broadway, New York.

Branch Offices.--Nos. 622 and 624 F Street, Pacific Building, near 7th Street, Washington, D.C.

Comments

Scientific American Supplement, No. 821, September 26, 1891Chapter V: Part 5

0%36 min left in chapter