84
ANALYTICAL
The three liquids were then run in the automatic instrument. Here, again, the castor oil was used as a calibrating liquid, and from the time in seconds obtained, and the specific gravities of the steel ball and castor oil, an instrument constant Kz was calculated thus: (3) Then
Kz =
'1.15
(7.79 - 0.958) 4.72
= 0.222
It is understood, of course, that K z is not the same function of T , p, I, and h as is K I , for i t is impossible to apply Ladenburg's corrections to the automatic instrument. The value of 0.222 obtained for Kz in Equation 3 was substituted in the formula 1 = Ka (4 - 4 ) tz (4)
EDITION
Vol. 6 , No. 1
stant-temperature baths. However, it is better suited than other viscometers to the automatic measurement oY the consistency of very viscous rubber cements, whether they are transparent or opaque. The instrument will yield results which are within the limits of variability encountered in rubber cement itself, as the data in Table I1 show. It will yield results quickly, actual times in seconds on the instrument being approximately equivalent to poises when the specific gravity of the liquid is about 1 and steel balls of 9.525 mm. (0.375 inch) diameter are used. The instrument requires only a small amount (350 cc.) of cement for one determination, and its operation requires no greater skill than the ability to turn three switches in correct sequence. The particular apparatus shown in Figures 3 and 4 has been used by factory operators over a period of 6 months at the time of writing.
ACKNOWLEDGMENT for the determination of the absolute viscosities of the samples The author thanks Norris Johnston and N. A. Shepard of corn sirup and Venice turpentine. I n 4 the value of tz is the time obtained on the automatic instrument. The for their many valuable criticisms and suggestions throughout the course of this work. summarized results are shown in Table 111. LITERATURE CITED TABLE111. COMPARISON OF ABSOLUTEVISCOSITIES OBTAINED ON FALLING-BALL VISCOMETER AND AUTOMATIC VISCOMETER (1) Broome, D. C., and Thomas, A. R., J. SOC.Chem. Ind., 50, 1 Automatic viscometer, seconds 2 Absolute viaoosities calculated from automatic viscometer times, poises 3 Absolute viscosities obtained from falling-ball viscometer, poises 4 Ratio between 2 and 3 a Mean of 9 determ+t/ons. b Mean of 6 determtnationa. 0 Mean of 3 determinations.
CASTOR CORN VENICE OIL SIRUP TWRPBNTINB 4.74 15.6b 11350
7.15
22.2
1710
7.15 1
19.9 1.115
1450 1 * 180
The results in Table I11 show that over a wide range of viscosities the automatic viscometer gives values of relative viscosity which, when corrected for the specific gravity of the liquid, are nearly proportional to absolute viscosity. The 18per cent error in the absolute viscosity of Venice turpentine and the 11.5 per cent error in the viscosity of corn sirup are no greater than should be expected when it is considered that Equation 3 applies strictly to only true falling-sphere viscometers, in which r is small with respect to p, and does not apply to the more complicated case of a ball rolling down an inclined V-shaped guide, as was assumed in Equations 3 and 4.
4241' (1931). (2) Gibson, W. H., and Jacobs, L. M., J. Chem. Soc., 117, 478 (1920). (3) Herschel, W. H., Proc. Am. SOC.Testing Materials, 19, 11, 677 (1919). (4) Jones, G., and Talley, S. K., Physics, 4, 215 (1933). (6) Knowles, D. D., Elec. J., 27, 116 (1930). (6) Knowles, D. D., and Sashoff, 5. P., Electronics, 1, 182 (1930). (7) Ladenburg, Ann. Physik, 22, 287 (1907); 23, 444 (1907). (8) Moore, L. P., and Cuthbertson, A. C., IXD. ENG.CHEM.,Anal. Ed., 2, 419 (1930). (9) Robinson, A. E., British Patent 330,042 (1929). (10) Sheppard, S.E., J. IND. ENQ.CHEM.,9, 523 (1917). (11) Symmes, E. M., and Lantz, E. .4.,Ibid., Anal. Ed., 1, 35 (1929).
RECEWSDSeptember 20, 1933. Presented before the Diviaion of Rubber Chemistry at the 86th Meeting of the American Chemical Society, Chioago, Ill., September 10 to 15, 1933.
Cleaning Platinum Wire for Flame Tests WESLEYG. LEIGHTON
TEMPERATURE CORRECTIONS For factory-control work, where rapidity in obtaining results is an important factor in the use of any instrument, it is not practical to measure the consistency of a rubber cement at a standard temperature, because of the difficulty of bringing the cement to that standard temperature within a reasonable time. For this reason, the automatic viscometer, instead of being equipped with an elaborate temperature control, was furnished to the factory operators with a temperature-correction table applicable to rubber cements of all consistencies actually met with in practice, and covering a range of temperatures greater than that normally encountered in the cement-house. CONCLUSION The automatic viscometer described in this paper is a simple, rugged instrument suitable for factory-control work where reliability of operation is of prime importance. It is not claimed that the instrument will give results with as high a degree of accuracy as certain other automatic viscometers, such as the one described by Jones and Talley (4),or as the manually operated Saybolt, Ostwald, or straight falling-sphere viscometers provided with thermostatically controlled con-
Pomona College, Claremont, Calif.
T
HE usefulness of potassium acid sulfate for removing persistent deposits from a platinum test wire seems to have been overlooked in textbooks on qualitative analysis, in spite of the fact that this very effective flux is commonly recommended for cleaning platinum vessels. In the hands of a student in qualitative analysis a platinum wire occasionally acquires a deposit which volatilizes sufficiently to contaminate flame tests, but which is removed with difficulty by hydrochloric acid and heat. In such cases it is more effective to use potassium acid sulfate. A coating of potassium acid sulfate is picked up by drawing the hot wire across a piece of the solid salt. On passing the wire slowly through a flame, the bead of potassium pyrosulfate which forms travels along the wire, dissolving the contaminating deposits. When cool, the bead is readily dislodged. Any small residue of pyrosulfate dissolves a t once in water, while the last traces are usually removed by a single moistening with concentrated hydrochloric acid, followed by heating. The clean, bright platinum resulting imparts no color to the flame. R ~ C E I Y EOctober D 14, 1933,
