Osmometer colloid

Simple osmometers have also been developed by Adair particularly for aqueous colloidal solutions. A thimblc-typc collodion membrane is attached to a capillary tube and contains the solution, When equilibrium is established the difference in level inside and outside the capillary is measured, Capillary corrections are made. For organic solvents a dynamic type osmometer may be used. A membrane of large surface area is clamped between two half cells and attached to each half cell is a fine capillary observation tube. With such an apparatus, equilibrium is rapidly established between solution and solvent contained in the half cells, The volume of the half cell may be small (about 20 cubic centimeters), The level of the solvent is usually aiiangecl to be a little below the equilibrium position, and the height of the solvent in the capillary as a function of time is measured, This procedure is repeated with the level of the solvent just above the equilibrium position. A plot is then made of the half sum of these readings. 

Because of their large molecular weight, proteins contribute only about 1 mOsmol/kg H2O to the total serum osmolality measured by freezing point depression. Occasionally, one may be asked to determine the contribution of macromolecules to the serum osmolality. Colloid osmotic pressure (COP) is a direct measure of the contribution of macromolecules (primarily proteins) to the serum osmolality. It is used primarily in the assessment of pulmonary edema or other abnormahties of water balance and serum protein concentrations. However, its utility has been questioned and the method is seldom used. Previous editions of this textbook describe the principles of a COP osmometer. 

All chemistries were determined by the clinical laboratory at the University of Utah Medical Center. A detailed error analysis shows the range of errors for clearance value to be between 10% at the start of dialysis and 15% at the end of dialysis. Oncotic pressures were measured with a colloid osmometer (Model 186, Instrumentation Laboratories, Boston MA) to 0.2 mm Hg. 

Osmometer An instrument for determining the osmotic pressure exerted by solvent molecules diffusing through a semipermeable membrane in contact with a solution or hydrophilic colloidal dispersion. See also Colloid Osmotic Pressure, Osmotic Pressure. 

Willibald Gottlob Schmidt (1828-77), a school teacher," found that animal membranes are less permeable to colloids than to sugar or salts. In (IV) Graham describes what he calls a dialyseVy based on his work on osmosis (see p. 652). He used a small bell-jar, formerly used as an osmometer , closed... 

Ultrafiltration and Osmometer. Small collodium sacks have been employed for some time by bacteriologists for filtering microbes. G. Mal-fitano was the first to point out that these sacks could be used with advantage in the investigation of colloids. The device is now in gen-G. Malfitano Compt. rend., 139, 1221 (1904). 

In order to free Congo Red from foreign electrolytes Bayliss precipitated it with HCl and dialyzed in a parchment osmometer until free from electrolytes In this manner he obtained a blue colloidal solution of the free acid that showed a very small rise in the osmometer. To get the sodium salt he dialyzed against a solution of sodium hydroxide, which caused an extraordinary rise in the osmometer. The excess of alkaU was removed by distilled water. After a week of dialysis the column retained a constant height of 50 mm. When the ordinary distilled water was replaced by conductivity water free from CO2 there was a further rise in the osmometer, and the column remained at 97 per cent of what it should from calculation. Only a faint cloud was to be seen in the ultramicroscope. The extraordinary sensitiveness to carbonic acid, as revealed by the last experiment, has also been observed by Biltz and v. Vegesack.f In these experiments membrane hydrolysis must be considered, which, according to Donnan, plays a part even in the case of strong electrolytes. 

From self-diffusion data, we have found that the structure is composed of closed droplets. NMR data and SANS data, analysed at higher q values, have demonstrated that the droplets have a concentration-independent size. The SANS data have also given us one size of the droplets, i.e. the hydrocarbon radius (and the shape), while collective and self-diffusion data have provided us with a value for the hydrodynamic radius. Knowing that we have identified a dilution line of spherical droplets of constant size, we can now turn to investigate the interactions. The latter affect properties such as osmotic pressure, diffusion and viscosity. The osmotic pressure, jr, can be measured, for example, in a membrane osmometer. A more common experiment for colloidal systems, however, is to measure the osmotic compressibility (97t/90) For a binary system, the osmotic compressibility is proportional to the structure factor at = 0, as follows ... 

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