B. — CHEMISTRY. 53" 



paper in the Phil. Mag. (5) I. and II., 1876, in wliich he states : 

 (i.) When a solution weaker than tlie cryohydrate loses heat, ice is 

 formed, (ii.) Ice continues to form and the temperature to fall until 

 the cryohydrate is reached, (iii.) At the point of saturation ice and. 

 salt separate simultaneously and the solid and liquid portions are 

 identical ia composition. 



These results can be expressed in the form of a simple diagram as 

 shown in the slide. 



In a subsequent paper, Phil. Mag. (5) 17, he extends his experi- . 

 ments to solvents other than water, and states that the substances 

 which separate at the lowest temperature are neither atomic nor mole- 

 cular; this lowest melting-point mixture of two bodies he names the 

 eutectio mixture. In the same paper he details the methods of obtain- 

 ing various eut-ectic alloys of bismuth, lead, tin, and cadmium. 



We have, in these papers of Guthrie's, the first important clue to 

 what occurs on cooling a fused mixture of metals. The researches of; 

 Soi'by and Guthrie, undertaken as they were for the sake of investigat- 

 ing natural phenomenal, are a remarkable example of how purely 

 scientific experiment can lead to most important practical results. It is 

 not too much to claim for these investigators the honour of being the 

 originators of all our modern ideas of metallurgy. Although much 

 valuable infonnation had been accumulated, no rapid advance could be 

 made until some general theory of solution had been developed. In 

 1878 Eaoult first began his work on the depression of the freezing- 

 point of solvents due to the addition of dissolved substances, and he 

 continued, at frequent intervals, to publish the results of his experi- 

 ments up to the time of his death in 1901. He established for organic' 

 solvents certain general laws: (i.) that for moderate concentrations the 

 fall of the freezing-point is proportional to the weight of the dissolved 

 substa.noe present in a constant weight of solvent; (ii.) that when the 

 falls produced in the same solvent by different dissolved substances are 

 compared, it is found that a molecular weight of a dissolved substance 

 produces the same fall of the freezing-point, whatever the substance is. 

 When, however, he applied the general laws which he had established 

 for organic solvents to aqueous solutions of inorganic acids, bases, and 

 salts, the results obtained were hopelessly disci'epant. In a paper in 

 the Zeit. Physikal. Chem. for 1888 on ' Osmotic Pressure in the 

 analogy between solutions and gases,' Van't Hoff showed that the 

 experiments of Pfeffer on osmotic pressure could be explained on 

 the theory that dissolved substances were, at any rate for dilute solu- 

 tions, in a condition similar to that of a gas ; that they obeyed the laws 

 of Boyle, Charles, and Avogadro, and that on this assumption the 

 depression of the freezing-point of a solvent could be calculated by 

 means of a simple formula. He also showed that the exceptions which 

 occurred to Eaoult's laws, when applied to aqueous solutions of 

 electrolytes, could be explained by the assumption, first made by 

 Arrhenius, that these latter in solution are partly dissociated into their 

 ions. The result of all this work was to establish a general theoiy 

 applicable to all solutions which has been widespread in its appli- 

 cations. It is true that Van't Hoff' s theory lias been violentlv attacked ; , 



