Intelligence and Miscellaneous Articles. 157 



CLEAVAGE OF COMPRESSED WHITE LEAD. 



7 St. Mary's Road, Canonbury, 

 My dear Tyndall, July 21, 1856. 



In an account of your lecture " On the Cleavage of Crystals and 

 Slate Rocks" (Phil. Mag. vol. xii. p. 46), you have noticed my ex- 

 perience in the consolidation of precipitated white lead, and have 

 correctly stated the unfavourable results of my first attempts with 

 conical moulds. It may be of interest to the readers of the Philo- 

 sophical Magazine to learn that the difficulty was entirely overcome 

 by substituting cylindrical moulds. By their employment the lateral 

 spreading of the mass was prevented, and cakes of white lead were 

 produced which broke with a conchoidal fracture, and which con- 

 sequently could readily be ground to a granular powder. 



I am. 



Yours very truly, 



Warren De la Rue. 



ON THE BEHAVIOUR OF IODIDE OF SILVER TOWARDS AMMONIA, 

 BY DR. A. VOGEL, JUN. 



The yellow precipitate furnished by iodide of potassium with ni- 

 trate of silver, is not dissolved by ammonia, but acquires a paler 

 colour therein. The author has found that this change of colour is 

 owing to a combination of the iodide of silver with ammonia. — 

 Buchner's Neues Repert. vol. v. p. 53. 



ELECTROLYTICAL INVESTIGATIONS. BY M. MAGNUS. 



It is well known that saline solutions do not follow the law of 

 equivalent decomposition by the galvanic current, as established 

 by Faraday, for Daniell found that they are decomposed in such a 

 manner that, besides 1 equiv. of acid and base, 1 equiv. of hydrogen 

 and oxygen are separated. Thus when a voltameter with dilute 

 sulphuric acid is interposed in the circuit together with the saline 

 solution, equal quantities of gas are evolved from both the saline 

 solution and the voltameter ; but besides this, the salt is decomposed, 

 and 1 equiv. of free acid is separated at the positive electrode, and 

 1 equiv. of free base at the negative. The decomposition in the saline 

 solution is therefore twice as great as that in the voltameter. 



To explain this remarkable phsenomenon, or bring it into agree- 

 ment with Faraday's law, Daniell found himself compelled to regard 

 sulphate of soda, not as consisting of base and acid in accordance 

 with the general view, but as composed of sodium with a compound 

 of 1 atom of sulphur and 4 atoms of oxygen. He gave the name of 

 oxysulphion to this compound, and was of opinion that all oxy salts 

 have a similar composition ; so that sulphate of copper must be 

 regarded as consisting of copper and oxysulphion, nitrate of potash. 



