February, 1924
INDUSTRIAL A N D ENGINEERING CHEMISTRY
pump of higher capacity is used, more air must be admitted to the system in the same interval of time, so that tubes d and e of greater diameters may be necessary in order to give a regulator of the same degree of sensitivity. When working with systems under pressures greater than atmospheric, the following slight modification of the regulator described should be made: Tube c is left open t o the air, while the reservoir g is closed with a rubber stopper hav-
161
ing three holes, two of which hold tubes d and e and the. third a tube 6 or 8 mm. in diameter, which is also connected by rubber tubing to the system under pressure. When this is in operation it allows excess air t o escape automatically into the atmosphere from the system. The diameters of tubes d and e should be chosen according to the sensitivity desired and the pressure pump capacity and the pressure desired in the system under control.
Surface Tension of Gelatin Solutionsls2 By Clarke E. Davis, Henry M. Salisbury, and M. T. Harvey NATIONAL BxscurT Co., Nsw YORK,N. Y.
The Morgan method has been used to determine the drop weighfs of gelatin solutions. These determinations are made with apparent ease f n concentrations up to nearly IO per cent when the temperature has been raised aboae the transition point giaen heretofore as 38 O C. Further eaidence of this transition point o f 38 O C. is found in drop weight measurements. Increasing concentration causes decrease in the drop weight.
With increasing temperature the drop weight increases in more concentrated solutions, but $nally shows decrease until the transition point is reached above which all concentrations show no appreciable change in drop weight. With increasing p H there is a tendency for all concenfrations to. reach a minimum at the neutral point. The drop weight changes slighfly with age of the solution.
EXPERIMENTAL APPmATus-The apparatus used was the Morgan drop weight apparatuslS with the exception that a manometer tube was included in the suction line to give an accurate control during the formation and falling of the drop of liQuid. Cottonseed oil was used in this tube because of its low weight Quinckea records the surface tension of one concentration. This measurement is undoubtedly in error, because the specific and low vapor pressure. The amount of suction used ab gravity of the gelatin solution a t 20’ C. is given as 1.0000, which the time when the drop fell was 0.47 mm. of mercury. is in error. METHODOF MAKINGDETERMINATIONS-The determinaDensity measurements have been made by Davis and Oakes. Zlobicki6 measured changes in surface tension of gelatin solu- tions were made in the usual mannerlo by collecting and weightions with temperature, making only a limited number of meas- ing a given number of drops, and from these the h o p weight urements, and reached a concentration of only 2 per cent gelatin. of the solution in milligrams was calculated. The agparatw
ERY few measurements of the surface tension of gelatin solutions have ever been made, and the few that are recorded cover such a limited range of working conditions that it was deemed advisable to measure the surface tension of gelatin solutions under varying conditions.
V
Bancrofts says, referring to Zlobicki’s work, “addition of 0.5
t o 0.S gram gelatin to 100 cc. water cause3 a marked decrease
in the surface tension of water, while addition of further amounts has practically no effect. In the same connection, Alexander’ says, “0.5 to 0.8 gram of gelatin to 100 cc. of water causes a marked lowering of the surface tension of water although further addition does not increase the effect.”
Consideration of Fig. 2 shows that increasing concentration of gelatin causes a continuous and appreciable decrease in the surface tension of water. Sheppard and Sweets measured the interfacial tension between gelatin solutions and toluene, but have made no measurements of gelatin solutions in contact with air.
The present paper covers an investigation of the variation of surface tension with (1) concentration, (2) temperature, (3) pH, and (4) age of solution. 1 Presented before the Division of Leather and Gelatin Chemistry a t the 66th Meeting of the American Chemical Society, Milwaukee, Wis., September 10 t o 14, 1923. * Contribution No. 8 from the Research Laboratory, National Biscuit Co., New York, N. Y . : A n n . Physik, 10, 607 (1903). 6 J . A m . Chem. SOL.,44, 464 (1922). 4 Bztll. acad. sci. Cracovie, 488 (1900). I “Applied Colloid Chemistry,” 1921, p. 189. 7 “Glue and Gelatin,” 1928, p. 138. a J. Am. Chcm. Soc., 44, 2797 (1922).
10
0 IO 20 30
-
40
1 I
1
2
3
4
5
6
7
8
9
1
0
1
1
PH FIG.1-TITRATION CURVE
FOR OSSElN
GELATINNa. 1. 1 P E R
CENT
SOLUTION
was thoroughly cleaned and dried before each determination. During the determination a constant temperature was maintained by use of a water thermostat. 9 J . A m . Chem. SOG., 82, 349 (1911). 10 Morgan and co-workers, J . Am. Chcm. Soc., 80 (1908); 35 (1911): 86 (1913),a series of some twenty papers.
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
162
The results in this paper are left in their original form as drop weights, for it is agreed that the Morgan method gives results which are experimentally accurate but it is not agreed as to just what correction, if any, should be made to calculate the surface tension; hence it is left to the discretion of the critic as to what correction formula should be used.
PERCENT
SOLUTION
FIG.2-VARIATION O F DROPWEIGHT WIT= STRENGTR O F SOLUTION OSSEINGSLATINNo. 1. pH 4.2 AND 8.0. 25O AND 40° C.
Harkins and Brown1' present an elaborate formula for this: DROPWEIGHTS OF KNOWN LIQUIDS Conductrvity Water Temperature
Weight
25 40
76.35 73.65
c.
25
Mg.
Benzene (Thiophene-free)
28.96
The diameter of the tip used was approximately 5.2 mm. METHODOF MAKINGGELATINSOLUTIONS-Gelatin solutions were always made according to the same procedure. Sufficient gelatin was weighed out and added to distilled water to give a certain percentage of gelatin in the finished solution. The solution was made by heating with stirring on an electric hot plate. Care was used to see that the solution came to definite temperatures after given periods of heating. The solution reached 75" C. in 20 minutes. It was then removed from the hot plate and adjusted to the desired pH by adding either sodium hydroxide or hydrochloric acid. 11
J . A m . Chem. Soc., 41, 499 (1919).
25
30
35
45
40
TEMPERATURE O C . FIQ.8-vARIATION OF DROPWEIQHT WITE TEMPERATURE OP 1 AND 3 PER CENT SOT.UTIONS 09 OSSEINGELATIN No. 1. pH 8.0
-
Vol. 16, No. 2
The amount of either of these necessary was predetermined by running a titration curve of the gelatin under examination. A typical curve of this sort is shown in Fig. 1. The solution was then filtered and finally brought to the temperature at which the determination was t o be made by placing it in the thermostat. Uniformity of procedure in making the solution was absolutely necessary in order to obtain results of value, as both the sol and gel forms were present.l2 Any deviation in the heating causes changes to take place in the character of the gelatin. HYDROGEN-ION DETERMINATIONS-These were made by means of the Clark and Lubs series of indi~ators'~ and by means of the hydrogen electrode using the method as described by Beans and Oakes.l4 RESULTS VARIATIONOF DROP WEIGHT WITH CONCEXTRATIONFig. 2 shows the relationship of drop weight to per cent gelatin in solution using ossein gelatin. I n the upper curves the determinations were made a t 25" C. The solutions were made a t pH 4.2 and 8.0. These curves follow each other closely, showing a marked decrease in drop weight with an increase in the percentage of gelatin. It was impossible to carry these determinations to a higher percentage of gelatin a t 25" C., owing to the formation of a jelly. This decrease in drop weight was found to hold in about the same relation a t several other p H values examined. The lower curve shows the effect of raising the temperature to 40" C. There was a marked Iowering of the drop weight in comparison with the 25" C. curve and determinations were made up to 8 per cent gelatin. There were indications that the percentage could have been carried even further, no jelly formation taking place because the temperature was high enough to insure the complete transition from the gel to sol form.4 VARIATION O F DROPWEIGHT WITH TEMPERATURE-Fig. 3 shows the relationship between drop weight and temperature, using two concentrations-namely, 1 and 3 per cent solutions. Examination of the curve for the 1per cent solution shows a marked decrease in drop weight until the temperature reaches 38" C., a t which point the direction of the curve changes abruptly and becomes practically a straight
.
Oakes, and Brown, J . Am. Chcm. Sor., 48, 1526 (1921). Clark and Lubs, J . Bact., 2, 1, 109, 119 (1917). J . Am. Chem. SOC.,42, 2110 (1920).
11 Davis, 18 14
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
February, 1924
line, showing no further change in the drop weight. The curve for 3 per cent solution likewise shows a decided change in direction of the curve a t 38" C. above which the drop weight value is practically constant.
163
It is to be noted that the original gelatin with its impurities lowers the surface tension more than the ash-free gelatin, and that the 1 per cent ash-free gelatin lowers the drop weight more than the 0.5 per cent solution, which agrees with the information shown in the curves giving the relation between concentration and drop weight. VARIATION OF DROP WEIGHTWITH pH-Figs. 5 and 6 show the variation of drop weight with pH a t concentrations of 0.5 and 1 per cent. 64
d f6l t
5 58
a
55
0
ESZLI
I
2
4
0
I
1
1
I
1
I
1
I
6 8 IO 12 14 16 18 AGE OF S O L U T I O NH-O U R S
FIG.7-VARIATION
20
I
I
I
22 24 26
OF DROPWEIGHT WITH AGE OF NO. 1 GELATIN
(BONE). pH = 4.2.
25°C.
VARIATION OF DROPWEIGHTWITH AGE OF SOLUTIONDrop weight measurements were made on 1 and 2 per cent solutions of bone gelatin a t a pH of 4.2 at 25" C. over a period of 24 hours, as shown in Fig. 7. Both solutions showed a slight decrease in the drop weight with age, and the curves themselves are approximately parallel. FIG..!#-VARIATION
OF DROPWEIGHT WITH pH O F 0.5 P E R CENT
SOLUTIONS AT 25' C.
Further evidence is here found for the existence of the transition point heretofore claimed as 38" C.4 In the 3 per cent solution there is a decided maximum around 30" C. Some evidence of this maximum also shows a t this point in the 1 per cent solution. PREPARATION O F ISOELECTRIC GELATIN-ISOeleCtTiC gelatin was prepared by the method described by Loeb.16 VARIATIONOF ISOELECTRIC GELATINWITH pH-Fig. 4 shows the relationship of isoelectric gelatin with pH a t 25" C. The isoelectric gelatin was made from hide gelatin No. 3. The curves show the relationship of the original gelatin with that of the isoelectric gelatin. The isoelectric gelatin can, of course, only be called isoelectric a t p H 4.7. When it is adjusted to p H values other than 4.7 it must be called ash-free. 16
J . Am. Chem. SOC.,44, 213 (1922).
Apparatus for Drying Gases' By V. T. Jackson 5701 BLACKSTONE AVE.,
CHICAGO, ILL.
H E piece of apparatus shown in the sketch has been found useful in drying gases. The small openings should be made from glass tubing having an internal diameter of 7 mm. The other dimensions are indicated in the sketch. A layer of glass wool p-3cm.4 + about 1 em. thick is placed in the bottom of --f the barrel so as to cover the two openings. Small glass beads are placed on top of the glass wool to a depth of about 10 em. Concentrated sulF' furic acid is poured over the beads until it rises about 1 cm. above them. The opening a t A is then closed with a rubber stopper. Connections are made so the gas can be aspi-
el
'=q
p-lt..-g
I
I
$
i
-1.
F I G 6-VARIATlON
OF ,DROPWElGHT AND pH OF
0.5 A N D 1
HIDEG E L A ~ INO. N 3.
PER CENT SOLUTIONS.25" A N D 40° C.
