it is this range also which possesses the greatest theoretical interest a t the present time. The measurements are summarized below concentration
osmotic pressure
0.00836 0.00539 0.00175 0.000474
278.7 186.0 63.5 17.5
(moles KC1 per 1000 gr. of water)
(mm)
The results obtained are in fair agreement with the values calculated from freezing-point determinations and the Debye-Huckel theory of complete dissociation. Applications The method of measuring osmotic pressure outlined may be applied along several lines which have not previously been possible. It is applicable generally to any non-volatile solute in a volatile solvent. As already indicated it can be applied to solutions of electrolytes and furnishes a means for investigating the activity of solutions a t extreme dilution and for testing the recently advanced hypothesis of complete dissociation. It is possible to apply i t to solutions of colloids, both lyophobic and lyophilic, which may throw much light on their character. Moreover, it can be used for other than water solutions; for example, solutions in organic solvents. I n contrast to freezing-point lowering or boiling-point raising determinations, measurements may be made a t any desired temperature. It should also be pointed out that this method of measurement has the advantage of using air-free solutions. The solubility of air in water under atmospheric pressure is nearly 0.001 mold, which may well have an appreciable effect on the activity of the solute a t low concentrations. In a study of the properties of solutions it should he possible to attain reliable information a t much greater dilutions through osmotic pressure measurements than through any other means, because of the much greater magnitude of this property. This is apparent if i t is noted that for a 0.001 mold solution of a uni-univalent electrolyte the freezing-point lowering is approximately 0.003G0 while the corresponding osmotic pressure is about 37 mm. Ultra-Violet Light Used as Test for Dirt in Milk. A German scientist, Dr. F. M. Litterscheid, has recently found that valuable information can be gained by examining milks by ultra-violet light. In this way he can decide whether dirt in milk is due to external contamination or to the milk itself. When coated with Japan lacquer, the vegetable residues from caw's excreta give a bright red luminescence which serves to distinguish them from the ordimary milk residues (casein or albumin curd), for the latter are not a5ected by the lacquer. Dr. Litterscheid considers that his method will prove to be of great value in the routine examination of milk.-Science Sereice
