TKANSACTIONS OF SECTION B. 535 



By applyinpr the theory of osmotic pressure (we Van 't IIofTs researches) there 

 can be caleuhi ted what fall ouj^ht to ho jiroduced when one molecular we'if^ht of a metal 

 is dissolved in a given volume of the solvent — in this case 11,8H0 gram-i of tin (for 

 formula, see I'rof. J. J. Thompson's * Ap])lication of Dynamics to Physics and 

 Chemistry,' § 1^1). The calculated fall is about 3° C. 



The authors infer from this that it is probable that the molecules of the 

 majority of metals when in solution in tin are monatomic, but that aluminium is 

 diatomic. 



It may be noted that E. Tamman of Dorpat has, by similar experiments, 

 come to the conclusion that v?hen in solution in mercury the molecules of metals 

 are monatomic, and that Professor llamsay has, by a ditlerent method, arrived at 

 the same result. 



The authors find that the metals are apparently independent of each other in 

 their action, as several metals can be dissolved at once in the same mass of tin, 

 and each metal will produce its own effect independently of the others present. 

 Hence we may conclude that Dalton's law of ' partial pressures ' liolda good in 

 these cases of osmotic pressure. 



G. The Manufacture of Prussiate of Potash. 

 By J. B. Readjian, D.Sc, F.R.S.E. 



The first port ion of this paper referred to the present condition of this manufacture, 

 describing the present process as very wasteful and imperfect, and showed that very 

 little attention has of late years been devoted to improving the process, which has 

 remained stationary for nearly half a century. 



A general sketcli of the process now employed in manufacturing prussiate was 

 next given. Then followed a brief notice of the history of prussiate since its discovery 

 last century, and of the processes that have been proposed or patented to improve the 

 manufacture, and lastly, full details of a series of experiments made by the author 

 to produce prussiate by the action of ammonia gas upon red-hot wood charcoal 

 which had been previously saturated with carbonate of potash. 



FRIDAY, SEPTEMBER 13. 

 The following Report and Papers were read : — 



1. Second Beport of the Committee on the present methods of teaching 

 Chemistry. — See Reports, p. 228. 



2. The Manufacture of Aluminium from Cryolite.^ 

 By Professor P. Phillips Bedson, D.Sc, F.C.S. 



After referring to the fact that the manufacture of aluminium formed the 

 subject of a paper read before this Section at the last Newcastle meeting, in 1803, 

 the author gave a description of the method of manufacture of this metal from 

 cryolite, which had recently been commenced on the Tyne. The production of 

 aluminium from cryolite by its decomposition with metallic sodium, dependent 

 upon the reaction, represented by the following equation, 



(NaF)3AlF3 + 3Na = Al + 6NaF, 



was first observed by II. Rose and the late Dr. Percy in 1855, but owing to the 

 difficulties associated with this decomposition it has until recently remained a fact 

 of scientific interest only. Professor Netto has, however, successfully overcome 



' Published in full in the Cluimical News, Oct. 25, 1889. 



