A magnetic suspension osmometer.

The magnetic suspension balance is used for the measurement of very small osmotic pressures. The apparatus is essentially the same as that previously used for the measurement of the density and viscosity of protein solutions except that the magnetically suspended buoy is modified to make it pressure sensitive. The method is especially useful for the measurement of osmotic pressure in small samples of dilute solutions (about 10(-6) M) or of substances with molecular weights greater than 10(5). A height-sensing device has been developed which is not dependent upon the visual precision of the operator.