180 Kkpokt S.A.A. Advanckment of 8ciknce. 



The bodies dissolved in a liquid — for instance, water — cause some 

 changes in the physical peculiarities of it, namely : — 



(1) The freezing-point of a solution is lower than that of the 

 solvent. 



(2) The steam pressure is lower, and of course 



(3) The boiling-point of a solution is higher than the solvent's. 

 The proportionality of these alterations to the concentration of 



a solution creates the possibility of finding the concentration by 

 determination either of the freezing-point or the boiling-point of a 

 solution. 



Beckmann introduced a handy a})paratus for measuring the depres- 

 sion of the freezing-point (A), 'ind it has proved to be ver}' useful for 

 research on organic liquids. 



The possession of cryoscopy in connectic»n with the knowledge of 

 se\ ei-al facts and relationships enables us to find the concentration and 

 osmotic pressure of a solution, namely : — 



(1) Solutions with the same depression of the freezing-point have 

 equal concentrations and the same osmotic pressure. 



(2) A solution containing one mole (molecular weight in grammes 

 pro litre) of a substance* shows a constant freezing-point of - 1-85° C. 

 By means of this fact it is possible to determine the molecular weight 

 of a substance by cryoscopy. 



(3) A solution of one gramme molecule of any substance (except 

 electrolytes) in 1000 grammes of water has an osmotic pressure of 

 22'34 atmospheres, or of one atmosphere when dissolved in 22*341 of 

 water. 



(b) Electkolytic Dissociation. 



Before entering into the results of cryoscopical examinations in 

 veterinary science, I have to explain another theory, closely con- 

 nected with Van 't HofF's theor}- of solutions, and supplementary to 

 it, namely, the doctrine of the electrolytic dissociation brought forward 

 by Arrhenius. 



In solutions of acids, bases and salts it was observed that they 

 had a lower freezing-point than had been calculated from the con- 

 centration. Arrhenius explained this anomaly as follows : — 



The molecules of salts, bases and acids in solution are partially 

 split up in two components, from which exery one exercises an osnaoti- 

 cal pressure and iniiuences the solvens like an entire molecule. These 

 components, called iont), are electrically difierent, and if two electrodes 

 are put in the solution, the negative ion, anioti, goes to the positive 

 pole, anode, the positive ion, kation, however, going to the negative 

 kathode. Tlie ions are giving away their respective electricities to the 

 corresponding electrode Avith the adverse sign. Acids in solution, for 

 instance, are characterised by the monovalent hydrogen ion ( + H), 



* All crv'stalloid water-soluble snl>.«taiices e.\'ce[>t the electrolytes, acids, 

 l>:i:-('s and salts. 



