Volume 4, Issue 6, 01 June 1933
Index of content:
4(1933); http://dx.doi.org/10.1063/1.1745180View Description Hide Description
The hydrostatic head correction as ordinarily made in viscosity measurements may be in error. This is made evident when one determines this correction at widely different pressures or with liquids of widely differing fluidities. It is concluded that this error is due to differences in the value of the coefficient m of the kinetic energy correction in different directions of flow. Such differences are due to departure of the capillary tube from a true cylinder which may have arisen in the manufacture of the capillary or of the viscometer. These differences in the value of m are so considerable that not only should the value of m for each viscometer be determined but a separate value should be determined for each direction of the flow through the capillary. Fortunately, this measurement is simple.
4(1933); http://dx.doi.org/10.1063/1.1745181View Description Hide Description
The specific volumes and fluidities of six isomeric hexadecyl alcohols and the corresponding hexadecyl acetates have been measured from 0 to 100°C where practicable. The associations of these liquids have been calculated and shown to be extraordinarily low. This suggests the importance of further studies on the association of compounds of high molecular weight and low association.
4(1933); http://dx.doi.org/10.1063/1.1745182View Description Hide Description
Measurements are made on the viscosity of aqueous solutions of barium chloride at 18°C over the range 0.006 to 0.492 molality. The value of the constant A in the equation η=η c /η0=1+Ac ½ is determined and found to agree, within 4 percent, with the theoretical value of the constant as determined by Falkenhagen and Vernon. The constants of several empirical equations are also given.
4(1933); http://dx.doi.org/10.1063/1.1745183View Description Hide Description
While examining the literature relating to the viscosity of aqueous solutions, the writer noticed some measurements obtained in connection with the viscosity of aqueous urea which appeared to warrant a reinvestigation of this substance. The relative viscosity of aqueous urea was accordingly measured at 18°C and 25°C over a range of concentration from 0.005 to 1.876 mol/liter. Fluidity— volume‐concentration curves exhibit negative curvature, evidencing that urea behaves like an electrolyte in that it decreases the fluidity of water less than would be expected on the basis of additive fluidities. It behaves like a non‐electrolyte in that it exhibits no stiffening effect; i.e., the value of the Falkenhagen constant A is zero. A table is included, giving a comparison of the observed and calculated values of the Falkenhagen constant A for 11 electrolytes.
4(1933); http://dx.doi.org/10.1063/1.1745184View Description Hide Description
A new method for the automatic measurement of the time of flow of a liquid in a viscometer of the Ostwald type by means of a photoelectric cell is described. The elimination of the psychological errors inherent in the older technique permits greater precision. Other sources of error in the use of the Ostwald viscometer are analyzed and the precautions necessary for precision viscometry are discussed.
4(1933); http://dx.doi.org/10.1063/1.1745185View Description Hide Description
An extrusion plastometer operating at rates of shear comparable with those existing in rubber tubing machines (10 to 1000 sec.−1) is described. The relation between efflux rate and pressure at constant temperature for various types of rubber stocks was determined. For highly compounded rubber stocks, such as tread stocks, the efflux rate vs. pressure curves attain linearity at low rates of shear. Both the slope of the curves and the extrapolated pressure intercept vary rapidly with the temperature, indicating that both the mobility and the yield stress are functions of temperature for highly compounded stocks. For lightly compounded stocks and for crude rubber, the curves are of the power function type at the lower rates of shear, but appear to attain linearity at the very high rates. These linear portions of the curves, for a given stock at different temperatures, are approximately parallel. Elastic recovery was determined as a function of rate of efflux. The slope of the recovery vs. efflux rate curves decreases with increasing rates of efflux. The relation between efflux rate at constant temperature and pressure, and time of milling, is approximately linear. The extrusion plastometer is shown to be more sensitive to overmilling than is the Williams plastometer. The partial failure of the compression‐type plastometer to correlate with the factory extrusion machine is explained on the basis of the much lower rates of shear employed in the compression‐type instrument than those existing in the extrusion machine.