Volume 15, Issue 8, August 1944
Index of content:
15(1944); http://dx.doi.org/10.1063/1.1770267View Description Hide Description
The construction of a vacuum microbalance having a sensitivity of 0.3×10−6 g, using a 0.6840‐g sample, is described. The pressure coefficient is found to be less than 0.3×10−6 g for a 1‐atmosphere change. The temperature coefficient is found to be 0.8×10−6 g/°C change. The zero point of the balance is found to be stable to better than 1×10−6 g over a period of 24 hours. The technique of measurements is briefly discussed. Several typical experiments on the formation of oxide films on iron at 25°C and 300°C are presented.
15(1944); http://dx.doi.org/10.1063/1.1770268View Description Hide Description
In the study of the thermodynamics of solutions it is desirable to measure heat effects (of the order of 0.001 cal.) which occur during the dilution of dilute solutions. In the Lange‐type calorimeter a thermopile of approximately 1000 junctions is used differentially. For this purpose a thermopile has been constructed using constantan‐Chromel‐P couples mounted in a sheet of Micarta, , and electrically insulated with a Vinylite resin which has an insulation resistance greater than 25 megohms. This instrument appears to offer somewhat better behavior than previously used units with respect to stability, sensitivity, and rapidity of response to temperature changes. The thermopile consists of two sections of equal numbers of junctions which are connected in parallel to a Leeds and Northrup HS galvanometer in series. At a scale distance of nine meters the sensitivity of the system is 0.25 microdegree per mm. Since one liter of diluent (water or dilute solution) is contained in each half of the calorimeter, this corresponds to a mean sensitivity of 2.5×10−4 cal./mm, with a probable error of the mean of ±0.03×10−4 cal./mm. The heat conductivity constant of the calorimeter is 0.004 min.−1 and that of the thermopile is 0.03 min.−1. Measurements with the present thermopile of the heats of dilution of sodium chloride solutions agree satisfactorily with wellestablished values.