ANALYTICAL EDITION
270
(17) Kremel, A., Notizen I. Prufe. d. Arzneimittel, p. 33, m. Berucksich der Herausgabe e. neuen osterreichischen Pharmacopoe, Frick. Vienna. 1889. (18) Marcusson, J., and Winterfeld, G., Chem. Umschau Fette, Ole, Wachse Harze, 16, 104 (1909). (19) Naael, W., and Komchen, M., Wiss. Yerdfentlich. SiemensK&zern, 6, 235 (1927). (20) Niegemann, C. N., Farben-Ztg., 21, 207 (1915). (21) Parker, W. B., J. Oil Colour Chem. Assoc., 5 , 197 (1922). (22) Parry, E. J., Chemist Druggist, 59, 689 (1901); 62, 175 (1903). (23) Richmond, G. F., Philippine J. Sci., (A)5, 177 (1911). (24) Richter, R., Pharm. Ztg., 59, 238 (1914). (25) Rudling, A., Chem. Rev. Fett- Harz-Ind., 10, 51 (1903). (26) Seltz, H., and McKinney, D. S., IND.EXQ.CKEM.,20, 542 (1928). (27) Sineh, P., Chem. Rev. Fetf- Harz-Ind., 18, 85 (1911); 19, 234 (1912); J . SOC.Chem. Ind., 29, 1435 (1910).
Vol. 5 , No. 4
Slack, H. F., Chemist Druggist, 87, 673 (1915). Steel, L. L., and Sward, G. G., J. IND. ENO.C H ~ M14,57 ., (1922). Stock, E., Farben-Ztg., 34, 1727 (1929). Umney, J. C., Phnrm. J.,(4) 21, 653 (1905). Whitmore, W. F., Weinberger, H., with Gardner, W. H., IND.ENQ.CHEM.,Anal. Ed., 4, 48 (1932). (33) Williams, R., Pharm. Zentralhalle, 30, 152 (1889). (34) Wolff, H., Chem...Rev. Fett- Hnrz-Ind., 21, 142 (1914); Chem. Umschau Fette, Ole, Wachse Harze, 28, 99 (1921); Farben- Ztg., 26, 1573 (1921); 27, 3130 (1922); Chem.-Ztg., 46, 265 (1922); Farbe u. Lark., 31, 245, 258, 269, 282 (1926). (35) Wolff, H., “Die Naturlichen Harze,” Wissenschaftliche Verlagsgesellschaft, m. b. H., Stuttgart, 1928.
(28) (29) (30) (31) (32)
RECFOIVED March 11, 1933. Contribution 7 from the Shellac Research Bureau of the U. S. Shellac Importers’ Association.
Glass Spheres for Viscosity Determination of Cuprammonium Solutions of Cellulose L. S. GRANT, JR.,AND W. M. BILLING, Hercules Powder Company, Inc., Hopewell, Va.
T
Large quantities of glass spheres, all of which that recommended by the CelluHE accuracy of the falltirne of fall through a standard lose Division of the AMERICAN have the ing-sphere m e t h o d for CHEMICAL SOCIETY and then to viscosity determination liquid, can be obtained by the method described make all other beads have the depends in a large m e a s u r e herein. Since all these spheres have fhe same on the degree of care exercised s a m e t i m e of f a l l t h r o u g h characteristics of fall in a given uiscometer, standard castor oil. The selecin the selection of the spheres used. they are particularly suited for those viscosity tion of such a standard sphere which require glass spheres, as, f o r and the method employed for When metal spheres are used, matching this s t a n d a r d with t h i s selection presents no example, cuprammonium solutions of cellulose. other spheres are described difficulties because of the unibelow. form aravitv of metal and the precisyon to” which such beads may be ground. I n certain SELECTION OF STANDARD SPHERE solutions, however, the use of practically all metals is proThe AMERICANCHEMICAL SOCIETY standard method calls hibited, because of the corrosive nature of the solution, the high specific gravity of the metal, or the opacity of the bead. for a glass sphere 0.125 inch (3.175 mm.) in diameter and Since this is especially true of cuprammonium solutions of having a specific gravity ranging between 2.4 and 2.6. The beads on hand, when difficulties were encountered cellulose, glass beads should be used for such viscosity work. I n the standard method for the determination of the in obtaining additional supplies, had a diameter of 3.17 mm. viscosity of cellulose as described by the Division of Cellulose and a specific gravity of 2.45. These spheres fell through Chemistry of the AMERICANCHEMICAL SOCIETY (I), a bead standard castor oil of 686 centipoises at 25’ C. in a standard of certain specifications is required. Glass beads when viscometer tube (A. C. S.) a t a rate equivalent to 22.3 centimolded or blown are not uniform in shape, size, or specific poises per second of fall. Since these spheres are well within gravity. The effect of these irregularities is overcome in the A. C. S. limit they were set up as the standard for comthe above method by calibrating each bead separately and parison of all future lots of beads. reporting the viscosky in poise;. This tediois procedure PROCEDURE FOR CALIBRATION leads to the use of a large number of spheres, each of which The essential steps in obtaining spheres which will give may have a different centipoise rating. The use of such spheres is obviously impractical where a large number is in the same time of fall as the standard sphere are as follows: constant use. selection from laboratory supply houses of glass beads In seeking t,o overcome such difficulties, it was found that approximately 4 mm. in diameter; segregation of these certain types‘ of glass beads can be ground to an exact di- beads by means of dense liquids into batches having narrow l i m i t s of specific g r a v i t y ; ameter with a great deal of and grinding these beads on precision. However, differ32 the basis of t h e i r a v e r a g e ent lots of glass beads vary 31 gravity to a diameter which widely in specific g r a v i t y has been d e t e r m i n e d from and quite often beads in the same lot will vary, in part 90 the Ladenburg modification because of different com29 of Stokes’ law (2, 3). positions of the individual SELECTION OF BEADS. The selection of the unbeads, and also because of 26 ground beads is im p o r t a n t the occlusion of small air bubbles. These conditions 27 because the H a r t f o r d Steel p r o m p t e d the a u t h o r s to 2 0 Ball Company, H a r t f o r d , 1. CORRECTION OF VISCOSITY SPHERE DIAMETER FOR Corm. , h a s f o u n d t h a t select a “standard” sphere of FIGURE SPECIFIC GRAVITYTO GIVE CONSTANTTIMEOF FALL not all b e a d s will s t a n d closer specifications than
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INDUSTRIAL AND ENGINEERING CHEMISTRY
July 15, 1933
grinding. When grinding beads for the authors, the company states that regardless of diameter the beads should be of regular shape and free from “tips,” surface chips, or other irregularities. It is also essential that the diameter be not greater than 4 mm., as otherwise too much grinding would be required for the ordinary specific gravities encountered in glasses. SEGREGATION OF BEADS. The segregation of any one lot of beads according to gravity is accomplished by the following steps: 1. Using 100 to 125 beads, determine the average specific gravity by weighing in a pycnometer. 2. Using the average specific gravity as the correct gravity, separate all the beads by placing them in a liquid of specific gravity 0.03 unit higher than the average gravity. All beads
which float are removed from the liquid and washed. Those beads which settle out are too heavy and may be discarded altogether, or saved and further separated, depending on the amount of beads. 3. Those beads which floated (step 2) are placed in a liquid of specific gravity 0.03 unit lower than the average gravity of the beads. All beads which float in this mixture can be discarded, while those which sink are recovered and washed.
The two liquids which have been found to work very well are tetrabromoethane (sp. gr. 2.95) and tetrachloroethane (sp. gr. 1.588). For any gravity between 1.59 and 2.95 calculate the amount of each liquid to use and mix in these quantities. The specific gravity will come out very close to its calculated value but to be on the safe side, the gravity should be checked by pycnometer. These liquids are good rubber solvents and should not be kept in rubber-stoppered flasks or used in equipment having rubber connections. The liquids are also volatile to a slight extent and should not be left exposed for great lengths of time. However, the gravity change while separating one batch of beads is not serious, as shown by the following figures : SP. GR. AT START 2.854 2.781
SP. GR. AFTER BEINQUSED A N D FILTERED 2,858 2.789
where q S
9@(1
3.2.4 ~ ) ( 1+ 3.3 ~ / h = ) 2g~’(di- du)T
viscosity of the liquid distance fallen through in time T T radius of the sphere dl density of the sphere do density of the liquid g acceleration due to gravity h height of liquid in the tube x = ratio of the radius of the sphere to the radius of the tube Grou ing the terms which are independent of specific gravity and ra&us, and solving for T , we get = = = = = = =
T = K (1
+ 2.4 x)(1 + 3.3 r/h) rYd1
- do)
Since the intention is to prepare beads which all give the same time of fall ( T ) ,then the expression (1
+ 2.4 x)(l + 3.3 r/h) +(di
- do)
for the standard bead must be equivalent to the same expression for the unknown. On substituting the fixed constants of the standard sphere and the viscometer, the equation becomes 1 0.357 T 0.0048 r2 rz(sp. gr. of bead - sp. gr. of solution) = 0.4317
+
+
For cuprammonium solutions of cellulose as the authors prepare them the specific gravity of the solution is 0,995. On the basis of this gravity Figure 1 shows a t once the diameter to which glass beads of any specific gravity must be ground in order to produce spheres equivalent to the standard in respect to time of fall. The calculated diameter must be closely adhered to, for it can be shown from the above equation that a 1 per cent decrease in the radius of a sphere a t constant specific gravity will increase the time of fall by 2.14 per cent. Results confirm these calculations. RESULTS
So far three lots of beads have been ground dom7n to a calculated diameter. The data on these three lots are as follows : LOT
The use of beads within the range 0.06 unit in specific gravity is based on the error introduced in the final viscosity measurements. It can be shown through a consideration of Stokes’ law that a 1 per cent variation in specific gravity a t constant radius introduces a 1.35 per cent error in the final viscosity. The 0.06 limit allows a total error in viscosity of 3 per cent or only * 1.5 per cent. A convenient arrangement for separating the beads after they have been placed in the liquid consists of a short piece of large-bore glass tubing, sealed off a t one end. The other end of the tubing carries a side arm of sufficient diameter to allow the beads which float to pass through. A quantity of liquid of the required specific gravity is placed in the large tube and a few beads are added. These beads are agitated a few times with a glass rod and when those which will settle have settled, more liquid is carefully added until the beads which float pass out through the side arm. The beads and liquid can be separated by pouring through a Gooch crucible. The liquid thus separated can then be used over again. The liquid may become dirty while in use, but it is easily cleaned by filtering through filter paper, The liquid which adheres to the beads may be easily removed by washing with either alcohol or ether. GRINDINQ TO PROPER DIAMETER. The proper diameter to which these beads are to be ground is calculated on the basis of the average specific gravity of the segregated beads. This is done by means of the Ladenburg modification of Stokes’ law:
271
Standard 1 2 3
SPECIFIC CALCULATED ACTUAL CENTIPOISES GRAVITY DIAMETER DIAMETER PER SECOND 2.45 2.77 2.81 2.74
Mm.
Mna.
2.81 2.77 2.845
3.17 2.795 2.82 2.84
...
22.3 22.4 23.2 22.33
It is seen that lot 2 fell 4 per cent too fast, the calculated diameter having been exceeded by 2 per cent. Other than this the results were very satisfactory, even though the diameter and gravity varied quite widely from the original specifications of the A. C. 8. method. CONCLUSIONS
It is possible and feasible to prepare, from beads having varying specific gravities, large quantities of beads all of which have the same time of fall through standard castor oil. Beads thus prepared will give just as accurate results as individually calibrated beads and after the selection of a standard bead, viscosity results may be reported in seconds or poises with equal accuracy. LITERATURE CITED (1) Committee on Viscosity of Cellulose, IND.ENG.CHEM.,Anal, Ed., 1, 49 (1929). (2) Hatsohek, “Viscosity of Liquids,” p. 35, Van Nostrand, 1928. (3) Ladenburg, Ann. Physik, 22, 287 (1907).
RECEIVEDFebruary 25, 1933. Presented before the Division of Cellulose Chemistry at the 85th Meeting of the American Chemical Society, Waahington, D. C., March 26 t o 31, 1933.
