Temperature control surrounding specimen

To favour reproducibility of results, the cycles of immersion and withdrawal must be kept the same from test to test. It is necessary to control the temperature and humidity of the atmosphere surrounding the test setup as these affect the rate of evaporation of the solution and of drying of the specimens when they are out of the solution. It is also necessary to provide for replenishing losses of water from the test solution resulting from evaporation. 

The damped oscillations are converted to an electrical signal by a non-drag optical transducer light is passed through a pair of polarizers, one of which serves as the inertial mass of the pendulum, to a photo-detector. The temperature, humidity and gas (usually helium) surrounding the specimen are closely controlled. 

Surface resistivity. One side of the specimen is coated with a circle of silver paint surrounded by a ring of silver paint. The uncoated distance between the circle and the ring is an effective length on which surface resistivity is measured. The other surface of the specimen is fully coated with silver paint. Current and voltage are measured and surface resistivity calculated. If samples contain internal or external antistatics, the measurement is performed under a controlled atmosphere to eliminate the influence of temperature and relative humidity. Also, specimen conditioning is used to account for migration of the antistatic to the surface. The surface of specimen containing antistatics is not coated with silver paint, but electrodes are... 

Temperatures above 4°K and intermediate to the normal boiling points of other liquids are obtained with a glass-reinforced plastic gas chamber having an open bottom. Filling the can with liquid then leaves gas surrounding the specimen. Power from individually adjustable autotransformers is supplied to each heater (S) on the upper and lower chucks as needed, and at the desired control temperature a dynamic balance is struck between the heat conducted to the specimen from the heaters and the heat removed radially through the gas space, the plastic wall of the gas chamber and the surrounding liquid. 

Although simple in concept, the adiabatic calorimetry method has numerous experimental problems associated with it. It is always difficult to match temperatures between a sample and its surrounding guard, which is especially critical in heat-capacity measurements. Furthermore, it is necessary to calibrate the specimen container. Both continuous and controlled step-change heating modes are employed, but both tend to be very slow as a quasiequilibrium state must be laboriously established at each temperature of interest. Finally, with polymer samples there may be problems in suitably casting or molding an electrical heater in the specimen. 

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