TRANSACTIONS OF SECTION B. 317 



its group are, therefore, isomorphous with didymiurn and not with cadmium, whence 

 it follows that the oxides of this group of metals are sesquioxides. The numerous 

 compounds of the yttrium metals prepared by M. Oleve are more simply formulated 

 on this assumption than on any other. 



The author exhibited a few specimens connected with this investigation. 



3. On the Synthesis of Hydrocyanic Acid. By Professor Dewab, F.B.8. 



4. On the amount of Nitrous Acid produced in Flectriq Illumination. 

 By Professor Dewab, F.R.S. 



5. On the Kinoline Bases. By Professor Dewab, F.R.S. 



6. An account of some Recent Experiments on Supersaturated Solutions. 



By John M. Thomson. 



In this paper the author alluded to his experiments communicated to the Chemical 

 Society, in which he shows that perfectly isomorphous substances, that is, bodies 

 possessing the same chemical constitution and crystalline form, are capable of ex- 

 citing crystallisation in supersaturated solutions of each other. Instances were 

 given of the different classes of salts examined, such as the sulphates of the Mag- 

 nesium group possessing the general form M''S0 4 7H 2 upon each other. Experi- 

 ments were also made on other isomorphous groups, such as the group of Alums, 

 and the phosphates and arseniates of sodium (Na 2 HPO t . 12H 2 and N« 2 HAs0 4 . 

 12 H 2 0). The author then alluded to experiments on mixtures of isomorphous and 

 non-isomorphous bodies with each other, pointing out that a considerable separation 

 between non-isomorphous bodies, when mixed, may be brought about ; but that 

 this separation could not be carried out with isomorphous substances. 



Mr. Thomson then described some new experiments upon the action of the dif- 

 ferent constituents upon supersaturated solutions of compoimd salts, such as the 

 action of potassium sulphate on an alum solution, the action of mercury iodide or 

 potassium iodide on the double iodide of mercury and potassium, the action of mer- 

 cury chloride or ammonium chloride on the double chloride of mercury and ammo- 

 nium, and finally the action of normal tartrate of potash or soda on a solution of the 

 compound salt, viz., rochelle salt. From these experiments it seems that in the case 

 of the double chlorides and iodides mentioned the different constituents behave as 

 active nuclei in exciting the crystallisation of the compound salts ; but that in the 

 cases of the alum and rochelle salt solutions, the different component salts were 

 not able to excite the crystallisation of the double salts. Mr. Thomson proposes 

 to extend these experiments, if possible, in the direction of an examination into 

 the condition of compound and double salts when in solution. 



7. Notes on recent Spectral Observations. 

 By J. Norman Lockteb, F.R.S. 



The following results have been obtained by the method recently described to 

 the Royal Society (Proc. R.S., vol. xxix. p. 266) :— 



1. Carefully distilled sodium condensed in a capillary tube, and placed in the 

 retort, gives 20 volumes of hydrogen. 



2. Phosphorus carefully dried gives 70 volumes of gas, chiefly hydrogen, which, 

 however, is not PH 3 , although it gives some of the lines of phosphorus. It is not 

 PH 3 , because CuSo 4 is not touched by it. 



3. Magnesium carefully prepared by Matthey is magnificent in its colourings ; 

 we get first hydrogen, then the D line [not sodium, for the green line is absent], 



