878
5
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y TABLE 111
Cure Hrs. 0.5 1 .o 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
True Free S 4.39 3.93 3.74 3.18 2.54 2.12 1.76 1.27 0.85 0.54
Sulfur in A1c.-KOH Extract 0.00 0.00 0.03 0.03 0.07 0.13 0.26 0.33 0.49 0.34
Coefficient of Vulcanization 0.61 1.03 1.21 1.63 1.93 2.30 2.51 2.88 3.14 3.54
Sulfur in Resin and S Compounds (Sol. in Acetone) (by Difference) 0.00 0.04 0.02 0.16 0.46 0.45 0.47 0.52 0.52 0.58
From these results i t is evident t h a t t h e theories of vulcanization proposed in t h e past, none of which took into account t h e formation of these compounds, are based on false figures and cannot be considered sufficiently accurate. SUMXARY
Two new methods for rubber analysis are presented. The first gives t h e correct value for free or elementary sulfur in rubber goods, and t h e second a lower and more accurate value for t h e coefficient of vulcanization t h a n can be obtained by any of the older methods. This work was all done on pure gum stock without any accelerator, and the methods developed are now being expanded t o meet t h e conditions which obtain in compounded stocks. DETERMINATION OF THE JELLYING POWER OF GELATINS AND GLUES BY THE POLARISCOPE1 By C. R. Smith FOOD INVESTIGATION LABOR.4TORY, BUREAUOR CHEMISTRY, DEPARTMENT OF AGRICULTURE, WASHINGTON, D. C. Received May 4, 1920
I n t h e commercial production of gelatins or glues, t h e raw materials, such as hides, bones, sinews, etc., after certain preliminary treatment, are extracted with hot water in several successive operations or runs a t successively higher temperatures. The first run or extraction, barring accidental changes or bacterial decomposition, yields gelatin of the highest jelly strength. The later runs diminish regularly in strength, probably because of the increasing time and temperat u r e t o which t h e raw material has been subjected. I n a previous paper2 i t was pointed out t h a t gelatins of the highest jelly strength approximated a definite a n d maximum value of mutarotation measured between 3 j " and 15' C. I t was early conjectured and observed t h a t the jellying power decreased in "weaker" gelatins parallel with t h e reduction of t h e mutarotation. The most probable explanation is t h a t this is due t o t h e decomposition of t h e gelatin molecules: i. e . , t h e percentage of actual gelatin which can exist in t h e two forms Gel form B Sol form 4 has been reduced. When t h e gelatin is practically all destroyed we have no mutarotation or jellying power and the product is the more or less indefinite &gelatin. The present polariscopic study of gelatins a n d glues correlated with certain physical tests including t h e "bubble standard" and mechanical devices, gives a good understanding of t h e relation of time, concentra1
Published by permission of the Secretary of Agriculture.
a J . A m Chcm. Soc., 4 1 (1919), 135.
Vol.
12,
No. 9
tion, and temperature in t h e development of jelly strength. The results obtained have suggested a standard of comparison for measuring jellying power, based on the polariscope, which minimizes t h e usual multiplicity of arbitrary conditions of t h e various mechanical testers in use. This paper does not discuss the many existing types of mechanical testers in use, for no one of them has been found t o be sufficiently widely used t o make a useful comparison with the polariscopic method. Comparisons have been made only with certain physical tests and contrivances which have been developed in t h e laboratory. I n extending t h e study of gelatins of t h e highest purity t o those of lower strength, it was thought important to. study the following points in evolving t h e polariscopic method: I-The constancy of the rotation per gram (or the specific rotation) at 35" C. a-The changing and final nearly constant and increased rotation per gram when cooled from 35" to 15" or 10' C. 3-The gelation increment of mutarotation based on the "bubble standard" of jelly strength. 4-Comparison of the polariscopic method with mechanical methods. The measurements reported in the previous paper were given in angular degrees. As most commercial laboratories are equipped with instruments using t h e Ventzke degree, the results are given in t h e latter unit. All readings are levorotatory. R O T A T I O X O F GELATINS A N D GLUES A T
35"
AND I j
"
c.
The samples were powdered and air-dried t o minimize the great sensitiveness t o changes in moisture, and TABLEI-ROTATION OF GELATINSAND GLUESAT 35' A N D 15' c. -Rotation after 6 Hrs. at 15' C -Rotation at 35' C.2 G. 5 G. 1 G. 2 G. 3 G. 5 G. 7 G. per per per per per SAMPLE per per 100 c c . 100 cc. 100 c c . 100 c c . 100 c c . No. 100 cc 100 c c . -9.0 -18.5 -28.6 -48.8 -68.8 13.40 -33.0 9.0 9.25 9.53 9.76 9.83 Per 6.70 6.60 9.6 19.8 30.3 52.2 73.2 13.50 33.60 9.6 9.9 10.1 10.44 10.46 Per gram. .... . 6 . 7 5 6.72 10.0 20.6 31.5 53.4 75.0 . . 13.40 33.5 861.. 10.0 10.3 10.5 10.68 10.71 Per gram 6.70 6.70 58.2 82.2 11.3 22.8 13.50 33.80 912.. 11.3 11.4 ... 11.64 11.73 6.76 Per gram 6.75 11.3 23.0 35.1 59.2 52.8 13.65 34.0 407.. 11.3 11.5 11.7 11.84 11.83 6.80 Per gram . . . . . , 6 . 8 2 11.6 23.5 35.7 60.8 85.4 13.70 33.7 171.. 11.6 11.75 11.90 12.16 12.20 6.74 Per gram 6.85 11.55 24.0 36.5 62.4 87.0 34.1 915 ,..... , 13.90 11.55 12.0 12.17 12.48 12.44 6.95 6.82 Perg-am. , . 12.0 24.50 37.1 63.0 87.0 12.0 12.25 12.36 12.60 12.43 12.1 24.60 37.1 62.8 87.6 34.5 864 ,....... 13.9 12.1 12.30 12.36 12.56 12.51 6.90 Per gram.. . . .. 6.95 12.15 24.7 37.7 63.0 88.0 671 . . 14.00 34.50 12.15 12.35 12.56 12.60 12.55 6.90 Per gram. . . . . , 7.00 12.5 25.5 38.8 65.2 91.8 33.5 406 . . , . . .. 13.50 12.5 12.75 12.93 13.04 13.10 6.70 Per gram., .. 6.75 13.0 26.55 39.9 67.2 93.0 34.5 859 ,..... . 13.85 13.0 13.27 13.30 13.44 13.3 6.92 6.90 Per gram.. 12.8 26.4 39.9 67.2 94.2 12.8 13.2 13.3 13.44 13.45 . 12.9 26.7 40.7 68.0 35.70 194.. , . . . . . 14.40 12.9 13.35 13.56 13.60 7.14 Per gram., . . .. 7.20 97.4 41.70 70.2 27.15 13.2 33.9 405.. , .. . , 13.75 13.57 13.90 14.04 13.92 13.2 6.78 Per gram ...... 6 . 8 7
-.
....
...
..... .
.
.. .
......
.
.. . ....
..
.
...
preserved in stoppered bottles. After soaking weighed amounts in cold water in graduated flasks for about 30 rnin. they were dissolved on t h e steam bath between soo a n d 60" C. and made up t o t h e mark a t 35". Rotations a t 3 5 " C. were measured in 2 dm. tubes after immersion in a water b a t h for 1 5 min. I t is preferable t o have t h e temperature a degree or so above 3 j " when
Sept., 1920
T H E J O U R N A L O F I N D U S T R I A L AiVD E N G I N E E R I N G C H E M I S T R Y TABLE11-MUTAROTATION AND
Minimum Amounts t h a t Produce Standard Jelly
NUMBER 0' C. 10OC. 15'C.
R o t . 'V. of Standard Jellies l o o C. 15O C.
JELLYING
Gelation Increment of Rot. O V., 3 G. per 100 Rotation V. Cc. in Equilibrium
____
POWER
Rot.Der Gram R o t . Der Gram a t 1d0 C. for
Mutarotation
____A__ _--A___
1 o o c . 15°C. 35O C. 15' C. 10' C.
879
150
c. 100 c.
mum Amt. 3 G. Conc. Conc.
Minimum Conc. Amt.
Conc. 3 G.
R Rot. o t . 35' 150
Bone Samples 436 166 86 1 192 195 912 407 171 858 864 67 1 742 406 915 191 859 194 169 168 405 393
1 2 3 5 6 7
8
9 10 11 12 A B
C
Sin I Sin C
1.40 1.60 1.15 1.25 1.10 1.20 1 . 0 0 1.10 0.92 1.05 0.81 0.86 0.70 0.78 0.70 0.78 0.70 0 . 7 5 0.68 0.73 0.67 0.73 0.70 0 . 7 5 0.62 0.67 0.65 0 : 6 1 0.65 0 . 5 7 0.62 0.62 0:57 0 . 6 2 0.53 0.56 0 . 5 3 0.56 0 . 5 1 0.54 0.50 0.62 0.76 0.57 0.63 0.52 0.74 0.83 0.77 0.86 1.15 1.10 ' 1.75 2.30 1.00 1.40
2.10 1.60 1.45 1.40 1.40 0.96 0.88 0.89 0.77 0.80 0.78 0.80 0.72 0.72 0.70 0.68 0.67 0.67 0.58 0.58 0.55
0.52 0.55 0.65 0.69 0.82 0.88 0 . 6 0 0.64 0.65 0.69 0.53 0.57 0.77 0.80 0.87 0.95 0.80 0.87 0.90 1.09 1.20 1.35 1 . 2 5 1.60 2 . 3 0 3.50 3 . 0 0 5.30 1.20 '1.35 1.80 2.60
-18.0 -20.4 14.8 16.6 14.3 15.7 13.8 15.3 13.3 15.0 11.2 11.3 10.1 10.8 10.6 10.7 10.5 10.0 10.0 10.1 9.9 10.1 10.3 10.2 9.6 9.4 9.2 9.6 9.5 9.5 9.0 9.3 9.2 9.5 9.0 9.4 8.5 8.5 8.4 8.5 8.5 8.4
8.2 9.6 10.9 9.0 9.5 8.0 10.6 11.3 11.0 11.4 14.4 14.4 21.8 25.8 14.6 17.7
8.4 9.5 10.7 9.3 9.5 8.4 10.1 11.3 11.1 11.8 15.0 16.2 29.3 40.3 14.8 22.3
7.2 6.4 6.3 6.2 5.9 5.4 4.8 5.4 5.2 5.0 4.8 5.1 4.8 4.8 4.9 4.7 4.8 4.7 4.6 4.6 4.7 4.6 5.1 5.1 4.7 5.0 4.4 5.4 5.4 5.4 5.2 6.2 6.0 6.8 6.8 6.6 6.1
6.4 5.9 5 9 5.6 5.2 4.9 4.8 4.7 4.8 4.6 4.7 4.8 4.6 4.7 4.5 4.6 4.7 4.7 4.5 4.6 4.6
-19.8 -30.2 -33.5 32.4 35.4 20.2 20.1 33.4 35.4 20.6 34.1 37.4 21.0 33.8 38.0 39.8 20.3 36.6 40.4 20.4 37.6 40.7 20.4 36.8 42.0 20.5 40.0 41.8 20.7 39.0 42.0 21.0 40.2 42.2 20.7 40.0 42.5 20.1 40.0 43.0 20.5 41.6 42.0 43.8 21.3 43.2 44.2 20.7 43.9 45.7 21.4 42.8 45.0 21.0 44.4 46.4 20.8 44.9 46.5 20.3 46.2 47.0 21.3 H i d e and Sinew Samples 45.0 46.0 20.9 4.6 42.6 41.2 20.7 4.7 41 . O 38.0 4.6 21.1 45.0 44.2 4.7 21.5 43.6 42.4 20.7 4.7 45.0 43.6 20.5 4.6 40.8 39.0 20.3 4.7 38.8 36.3 20.4 4.9 40.6 38.4 21 .o 5.0 39.0 36.2 4.9 20.6 36.9 33.2 5.4 21.3 34.6 31.8 20.2 5.5 28.6 25.6 19.6 6.4 26.0 19.0 22.9 6.8 37.4 34.0 20.0 5.8 29.6 27.2 19.3 5.6
working in a cold room so t h a t t h e temperature of reading does not fall appreciably below t h e correct temperature. When t h e solutions are cooled t o I j' C. t h e changes in rotation parallel t h e increase in viscosity. -4s was shown in t h e previous paper, t h e reaction is essentially bimolecular, and we find t h a t t h e rotations per gram of different concentrations change more rapidly in t h e higher concentrations, b u t as t h e change proceeds they approximate each other. The samples of Table I are supposed t o be made from ossein stock. They represent only a small proportion of those examined, proving t h e conclusions applicable t o gelatins and glues from hides, sinews, and other sources. Similar results have been obtained on many other samples and lead t o t h e conclusion t h a t t h e rotation per gram at 35' C. is nearly constant on all gelatins and glues. T h e results show t h a t a t t h e end of 6 hrs. t h e rotation per gram of various concentrations a t I j o C. approach each other, b u t t h e lower concentrations of I g. and z g. per I O O cc. are still somewhat slower. MUTAROTATIOiT A N D J E L L Y I N G P O W E R
If t h e solutions are maintained at I j o (or 10') over night ( I z t o 18 hrs.) t h e rotations finally reach constant values and represent t h e maximum change in rotation and jellying power a t t h a t temperature. These represent equilibrium rotations and corresponding equilibrium jellys trengths. The results given in Table I1 are particularly concerned with these equilibrium rotations and their corresponding jelly strengths rather t h a n t h e development produced in a definite and comparatively limited period of time. I n this table are assembled the results obtained on 40 samples of gelatins and glues arranged partly in t h e order of their jellying power and partly according t o origin.
10.4 12.2 13.3 13.5 12.8 16.3 17.2 16.4 19.5 18.3 19.2 19.3 19.9 21.1 20.7 22.5 22.5 21.8 23.6 24.6 24.9
13.7 15.2 15.3 16.7 17.0 19.5 20.0 20.3 21.0 21.1 21.0 21.5 22.4 22.5 22.5 23.5 24.3 24.0 25.6 26.2 25.7
9.7 10.4 10.8 10.9 10.7 11.8 12.3 12.0 13.0 12.6 13.0 12.8 13.0 13.3 13.6 13.8 14.2 14.0 14.7 14.7 15.3
10.1 10.8 11.1 11.4 11.3 12.2 12.5 12.2 13.3 13.0 13.4 13.3 13.3 13.8 14.0 14.4 14.6 14.3 14.8 15.0 15.3
11.2 11.8 11.9 12.5 12.6 13.0 13.0 13.6 14.0 13.7 13.6 13.7 14.3 14.1 14.6 14.5 14.8 14.8 15.2 15.3 15.7
11.2 11.8 11.8 12.5 12.6 13.3 13.5 13.6 14.0 13.9 14.0 14.1 14.2 14.3 14.6 14.7 15.2 15.0 15.4 15.5 15.6
1.53 1.60 1.66 1.66 1.68 1.80 1.84 1.80 1.95 1.88 1.91 1.94 1.99 2.03 1.99 2.09 2.06 2.04 2.14 2.21 2.14
24.1 20.5 16.9 22.7 21.7 23.1 18.7 15.9 17.4 15.6 11.9 11.6 6.0 3.9 14.0 7.9
25.1 21.9 19.9 23.5 22.9 24.5 20.5 18.4 19.6 18.4 15.6 14.4 9.0 7.0 17.4 10.3
15.3 13.7 12.2 14.6 13.8 14.7 12.9 11.9 12.9 11.8 11.1 10.1 8.6 7.6 11.0 8.5
15.0 13.7 12.7 14.7 14.1 14.7 13.0 12.1 12.8 12.1 11.1 10.6 8.5 7.6 11.3 9.0
15.7 14.7 13.3 15.0 14.6 15.1 13.7 13.0 13.7 12.7 12.0 11.5 9.5 8.6 12.1 9.8
15.3 14.2 13.7 15.0 14.5 15.0 13.6 12.9 13.5 13.0 12.3 11.5 9.5 8.6 12.4 9.9
2.15 1.99 1.80 2.06 2.05 2.12 1.92 1.78 1.83 1.75 1.56 1.57 1.31 1.20 1.70 1.41
In the first three columns results are given the minimum amounts in grams per IOO cc. which will produce the standard jelly a t o', IO', and 15' C., respectively, when the maximum strength has been developed. The standard jelly is such that a bubble of air 4 to 5 mm. in diameter admitted to the polariscope tube moves vertically with a scarcely perceptible motion of 4 cm. per second. It is sufficient to maintain the solution in a constant temperature bath over night ( 1 6 hrs.). No appreciable change in viscosity or optical rotation takes place on extending the time indefinitely. In the next two columns are given the rotations in ' V. of the standard jellies obtained with the corresponding minimum amounts of the two preceding columns. In the sixth and seventh columns are given the increments in rotations obtained by subtracting the rotations of the respective minimum amounts a t 3 5 O , calculated from the rotations of the 3 g. concentrations a t the same temperature given in the eighth column, from the rotations of the standard jellies at their respective temperatures. In Columns 9 and I O are given the mutarotations between 35 ' and 15' C., and between 35' and IO' C., obtained by subtraction of the respective rotations. In the next two columns are given the increments in rotation between 35' and 15' C., and between 35' and IO' C., obtained by subtraction of the respective rotations. In the next four columns are given the calculated rotations per gram based on the minimum amount concentration and the 3 g. concentrations a t I O O and 15' C. In the last column is given the ratio of rotation at 1 5 to ~ the rotation a t 35' C. The bone samples are known t o be so on representation a n d by odor. Those given as hide or sinew samples were obtained directly from t h e manufacturers by special arrangement. Only t h e last two samples are sinew samples and are designated Sin I and Sin C. Selecting Sample 405, for example, 0 . j 3 g. per I O O cc. just produces the standard jelly a t 0'; 0.56 g. per IOO cc. is necessary a t I O ' ; and 0.j8 g. a t I j' C. I n
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
880
these concentrations t h e standard jelly persists indefinitely. The rotation of 0.56 g. in t h e condition of t h e standard jelly is -8.4' V. a t IO'. The rotation of 0.58 g. a t 15'c. is 8.5' v. 0.56 g. of Sample 405 a t 35' rotates -3.7' V. (calculated from 3 g. per IOO cc. a t 35 '), hence t h e increment of rotation is 8.4 - 3.7 or 4.7' V. (corresponding t o 0.81 circular degrees in I dm. tube). Similarly t h e increment a t 1 5 ' C. is 4.6' V. Three grams of Sample 405 per roo cc. rotate -20.3 a t 3 j 0 C., -44.9 a t 15', and -46.5 a t IO' C., which gives us 24.6' V. a n d 26.2 ' V. as increments a t I 5' a n d IO' C., respectively. The rotation per gram a t 15' C. is -I 5 . 0 (14.96) ; calculated from 3 g. concentration, -15.0 (14.96); and t h a t calculated from 0.58 g. a t 15' is -14.7. Similarly t h e rotation per gram a t IO' C. calculated from 0.55 g. concentration is - q . 3 as compared with 3 g. concentration of -15.5. The samples showing the greatest mutarotation in the 3 g. per IOO cc. concentration require t h e smallest amounts t o produce t h e standard jelly. As t h e mutarotation decreases, t h e amounts required t o produce the standard jelly increase. Some of the "strongest" gelatins show about 8 per cent increase in strength passing from 1 5 ' t o 0 ' C., and about 4 per cent from 1 5 ' t o IO'. I t will be noted t h a t the rotations a t 35' C. of 3 g. per IOO cc. of air-dry samples vary between -21.5 and -19.6 ' V., decreasing ratherirregularly from t h e "strong" gelatins t o t h e "weak" ones. Probably this irregularity is due t o variations in ash and moisture content. I t is t o be noted t h a t t h e gelatin increment of rotation is approximately 4.6 t o 4.7 a t 1 5 ' or I O ' C. in t h e strongest gelatins. For these, their jellying power between Ij' and IO' (and probably a t 0') varies inversely as t h e extent of their mutarotation. We may make t h e highly probable assumption t h a t in more concentrated solutions t h e same ratios of strength will be preserved. I n t h e weaker gelatins t h e increment of gelation increases gradually d p t o about 7 . 2 in t h e weakest gelatin. It is obvious t h a t t h e inverse relation does not hold in these gelatins if compared with much stronger gelatins for t h e apparent mutarotation is greater t h a n t h e jelly strength developed would indicate. I n t h e weaker samples, a large proportion of nongelatin substance might either increase or decrease t h e t r u e mutarotation. T o study this point, comparison was made between Hide I and Hide C gelatins, cooling them rapidly from 35' t o 15' C. in t h e minimum amount quantities. T h e following readings were obtained : Rotation at 35O C.
. . ... .
H i d e 1 .... , . -3.8 Hide C .... , , , , -33.5
...
1 Min. 15OC.
2 Min. 15'C.
3 Min. Equilibrium 15OC.
15'C.
-3.8 -34.8
-3.9 -34.8
-3.9 -34.9
-8.4 -40.3
These results show t h a t t h e great change in rotation of Hide C, a t t h e end of one minute, which does not represent t r u e mutarotation, accounts for a change of about 1.3 points. This subtracted from t h e observed increment of 6.8 as given in the table gives us 5.5 points of t r u e mutarotation. T o test this point further, a sample of gelatin was heated in solution for
Vol.
12,
No. 9
several days until a 50 per cent solution would not produce a gel. This was examined polariscopically and showed little or no mutarotation, but a great increase in levorotation, when cooled between 3 5 ' a n d 15'. I t is quite evident t h a t our apparent gelatin increment of mutarotation is increased b y t h e change in t h e P-gelatin present in increasing amounts as t h e jelly strength diminishes. POLARISCOPIC METHOD A N D APPLICATIONS
The writer has selected I 5 ' and I O ' C. as standard temperatures for jelly strength comparisons rather t h a n higher temperatures which represent more active equilibrium between t h e sol and gel forms. This is apparent from the results a n d figures of melting points on gelatins of high jellying power in t h e previous paper a n d is even more pronounced in weak gelatins or glues where we find considerable difference in t h e strength developed even between IO' a n d 15' C. Further, t h e chest or "cool place" in which food gelatin may be set and preserved is not likely t o be higher t h a n I 5 '. I n grading gelatins or glues, polarize 3 g. per I O O cc. a t 3 5' t o 36 ' C. in a 2-dm. tube; cool a portion of t h e solution rapidly t o 15' (or IO') and transfer before t h e sample has jellied t o a cold I-dm. tube. This procedure avoids contractions in t h e jelly wfiich may 'produce poor readings. If t h e samples need clarification digest t h e solution with 5 cc. of light powdered magnesium carbonate a t 30' t o 40' C. for one hour or longer, and filter until clear, avoiding appreciable evaporation. Occasionally i t has been found advantageous t o a d d 0.10 g. of ammonium citrate t o the filtrate t o avoid t h e formation of insoluble calcium compounds, but this does not appear t o be necessary if t h e magnesium c;trbonate has been used in sufficient quantity and t h e digestion has not been too short. The procedure for clarification outlined has not been found t o change the polariscopic results when applied t o clear samples. I n place of a constant temperature b a t h t h e tubes can be placed in a large vessel of water in a portion of t h e ice chest where t h e temperature ranges between 13' and 16' and left over night. T h e next day t h e temperature can be controlled for 4 t o 7 hrs. at 15 =t0.4'. If a constant temperature b a t h is used t h e tubes may be read a t once in t h e morning. Considering a sample which polarizes --20.5' at 35' C. and -40.0' a t 1 5 ' C. in a concentration of 3 g. per I O O cc., i t is suggested t h a t t h e strength be expressed as 19.5 points a t 1 5 ' C., t h e increment in rotation in Ventzke degrees. Referring t o Table I1 we see t h a t a 25-point gelatin a t 15' represents t h e maximum strength obtained. I n factory control t h e jelly strength determinations can be made by t h e polariscope in t h e progress of t h e extractions, evaporation, or drying. T h e solutions are diluted t o approximately 3 g. per roo cc., controlled by rotations a t 35' C. T h e jelly strength a t 15' is determined as usual a n d calculations made by simple proportion t o reduce rotations t o a n average basis of -20.5' V. a t 35' C. An actual test in factory control gave t h e strength of a first extraction as I 7 points a t I 5 ' C. ; after evaporation. i t was I O points. T h e evaporated extract was mixed with some unevaporated material bringing t h e strength
Sept., r 9 2 o
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
t o 11.5 points; after dryingit tested 1 1 . 6 points. These figures obviously represent poor extraction, and considerable loss of strength in t h e evaporator, b u t show no loss from bacterial action in drying. Jelly strength tests made on samples direct and after incubation for 24 hrs. a t 37' C. show little or no loss in strength of nearly sterile gelatins, while those in active state of decomposition show considerable loss with t h e development of bad odors. The following results illustrate this : 35' C. 3 G . per 100 Cc. l... . . . -20.3 2 ....... -20.5 3.. . . . . -20.3
No.
Rot. at 15' C. Rot. at 15' C. before after Incubation Evaporation -33.4 -33.8 -36.8 -39.7 -31.6 -35.6
JELLY
STRENGTH
MEASUREMENTS
BY
A
reduction of pressure is produced (6 dm. of water), which causes a depression in t h e jelly which can be measured by a micrometer depth gage reading t o thousandths of a n inch. Some results are given in Table 111. TABLE111-MECXANICAL TWTS AT 10' C. Displacement in Inches Rotation Sample by Partial Vacuum Increme-it No. 6 Dm. Water 100 c. 393.. . . . . . . . . . . . . . . . . 0.137 25.7 25.6 168 .................. 0.135 20.0 407 0.269 23.5 859 .................. 0.218 1 0.136 25.1 7 . . . . . . . . . . . . . . . . . . 0.151 24.5 24.0 169... . . . . . . . . . . . . . . . 0.220
.................. ..................
Odcr after Evaporation Sweet Bad Bad
The solutions were filtered through magnesium carbonate t o clarify. The increase in rotation in No. I was probably due t o evaporation and experimental error. The loss of jelly strength in Nos. 2 and 3 was quite pronounced, with corresponding production of disagreeable odors. A progressive increase in levorotation (or mutarotation) obtained from a solution cooled quickly below 3 j" C., accompanied by t h e production of a jelly after a change of approximately 4.7 ' V., is very positive proof of t h e presence of gelatin in any solution concentrated enough t o jelly. MECHANICAL
TESTER
Several different mechanical testers have been developed in t h e laboratory but only one, which recommends itself as accurate and requiring a small amount of sample, is here described. The bubble test is accurate t o about 3 per cent on high strength gelatins comparing quantities which just produce t h e standard jelly. We have seen t h a t t h e minimum amounts necessary for jelly production change in a definite way following t h e mutarotation. I t was thought desirable t o make certain t h a t similar relations existed in much higher concentrations. Fig. I represents an 80 mm. glass funnel with short stem accurately formed t o a 60' angle. Mercury weighing 1 2 0 g. is poured into t h e funnel closed at t h e end. The diameter a t t h e surface of t h e mercury is 3 cm. Fifty cc. of t h e gelatin solution are poured over t h e mercury and allowed t o solidify in a horizontal position (determined by spirit level) i n a constant temperature bath a t 10' C. We have now formed S u c t i o n + Manometer a definite sized reFIG. 1 producible jelly in t h e shape of t h e frustrum of a cone. When t h e jelly is t o be tested t h e mercury is allowed t o run out and t h e jelly is connected with a water manometer, and a definite
881
SOME PHYSICAL CONSTANTS OF PURE ANILINE' By C. L. Knowles EASTERN LABORATORY, E. I.
DU
PONTDE NEMOURS & Co., CHESTER, PA.
The importance of aniline t o t h e dye industry has long been recognized, b u t no practical method of analysis has been available for general use in judging its quality. An attempt has therefore been made t o find a method of analysis or test which would not only be accurate, but of such a nature t h a t i t could be applied quickly and easily in t h e control of t h e manufacture of this product. A survey of chemical methods of analysis disclosed t h e fact t h a t , due t o t h e rather large experimental errors, most of them fail when t h e purity of t h e aniline exceeds 99. j per cent. Attention was therefore turned t o t h e possibilities of t h e application of t h e physical constants for accurately judging t h e purity. It would naturally be expected t h a t t h e physical constants of such a common intermediate would long since have been established beyond any reasonable question. As a matter of fact, a great number of investigators have made a study of aniline but, instead of establishing these points, widely diverging results have been published. On consulting t h e literature, no less t h a n 1 6 different values for t h e freezing point of aniline were found. These varied between -8' and -5.96 ' C. , whilg values for the boiling point ranged from 182.5' t o 184.8' C. Of t h e gumerous results given, t h e on$ ones considered were those in which t h e method of purification and methods of recording temperatures were fully described. The following have been chosen as most reliable, and are those generally accepted : Ampola's freezing point of - j . g 6 " , Timmermans' of - 6 . 2 0 ' ~ and t h a t of Jones and Sanderson of -6.00' C. The latter has been published since t h e completion of this work, along with a formula for determining the purity of aniline from its freezing point. Timmermans, Callender, and Beckman apparently give the most accurate boiling points, their results being 184.40 O , 1 8 4 . 1 0and ~ ~ 184.30' C. Since no conclusions could be drawn from these results, i t was necessary t o prepare a sample of pure aniline, and t o determine accurately its physical constants. In t h e course of this work i t was soon discovered why so many different values had appeared for t h e physical constants of aniline, since t o purify
L +
1 Presented at the 59th Meeting of the American Chemical Society, St. Louis, Mo., April 12 t o 16, 1920.
