Osmometer, electronic membrane

Some efforts are necessary to keep the osmometer imder appropriate working conditions. This relates mainly to the proper preconditioning and installation of the membrane, the attainment of thermal equilibrium, the caUbration of the electronic output, the adjustment of solvent zero, and to choosing the desired sensitivity. 

The breakthrough came in the early decades of this century, mainly through the adoption of physical methods, such as improved optical devices like the ultramicroscope, and the application of the ultracentrifuge, of new viscometers, osmometers, diffusion cells, and most of all, through the systematic appUcation of x-ray and electron diffraction to fibers, membranes, and tissues. A decade of intense research on cellulose, proteins, rubber, and starch wound up with the following fimdamental results ... 

An osmometer adapted for rapid measurements of osmotic pressure using small volumes of sample was design as above by Rowe and Abrams in 1957. The U-tube has a semi-permeable membrane arranged in its arm B which holds the protein solution (sample) above it while the solvent lies beneath it. Arm A also contains the same solvent. In the horizontal portion of the tube lies a very thin platinum foil which is connected further to a mechano-electronic transducer in circuit with a galvanometer. A controlled air pressure is continuously exerted on the protein solution. 

As a general feature of most osmometers, the membrane is clamped into a stainless steel thermostated chamber (the measuring cell and the pressure measuring system of modem osmometers are built into a high-grade electronically stabilized thermostat) and serves as barrier between the pure solvent and the polymer solution sides of the chamber. The solvent side (bottom) is in juxtaposition with a pressure sensor, e.g., the diaphragm of a capacitance strain gauge or a piezo-chip. The solvent transport is measured across the... 

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