194 ANNUAL OF SCIENTIFIC DISCOVERT. 



heat lost in its liquefaction, we perceive that it will rapidly cool the 

 vessel which contains it and, consequently, the neighboring material. 



To undertake the method of putting these principles in operation, we 

 have only to suppose an apparatus composed of two retorts soldered to- 

 gether by the necks, the whole perfectly close and without communica- 

 tion with the outer air. In the larger of these retorts, we place a 

 concentrated solution of ammonia in water and heat it. Driven off by 

 the heat, the gaseous ammonia cannot escape without becoming lique- 

 fied in the small retort. 



Reduction of C kl or id e of Silver. MM. Millon and Comrnaille have 

 communicated to the French Academy of Sciences an extremely ele- 

 gant reaction, by which absolutely pure metallic silver may be precipi- 

 tated from its ammoniacal combinations, with all the accuracy necessary 

 for rigid analysis, and in such a division as to render it available in the 

 arts. 



The reagent employed is ammonio-subchloride of copper. When 

 this substance is added to ammonio-nitrate or ammonio-chloride of silver, 

 the whole of the silver is at once thrown down in the metallic state as 

 a gray amorphous precipitate. The precipitate readily assumes a me- 

 tallic lustre under the burnisher, and may be applied to the surfaces of 

 wood, stone, etc. The reaction takes place so perfectly that it may 

 be employed either for the estimation of silver, or for the analysis of 

 a mixture of sub and protosalt of copper ; every atom of silver thrown 

 down representing one atom of sub-chloride of copper. It is, however, 

 especially valuable for reducing the chloride of silver residues of the 

 laboratory. These are dissolved in ammonia, and the ammoniacal sub- 

 chloride of copper added, when the metallic silver is at once obtained 

 in its purity. Moreover, it is only necessary to digest the filtrate with 

 a little powdered zinc in a closed flask, in order to reduce again the 

 copper salt, and it is ready for a fresh operation. In this way, the same 

 quantity of copper solution suffices for an indefinite number of precipi- 

 tations. 



Tinned Lead Pipes, etc. At a late meeting of the Liverpool Chem- 

 ists' Association, specimens of lead pipe and sheet-lead, electro-plated 

 with tin, were exhibited by Mr. Holt, and some discussion ensued re- 

 specting the use of lead coated in this manner for water cisterns and 

 pipes. It appeared to be the opinion of the meeting that a coating of 

 tin, instead of preserving the lead, was far more likely to ensure its 

 more rapid corrosion ; for if the coating of tin by any means happened 

 to be scratched off, even to the slightest extent, galvanic action would 

 take place, and the lead would be destroyed very quickly. Dr. Nevins 

 and Dr. Edwards stated that their experiments had proved that such 

 would undoubtedly be the case ; Dr. Edwards remarking that in one 

 case which he had examined, a cistern made of lead, in which was an 

 accidental admixture of tin, was eaten out by well-Avater in six mouths, 

 the lead being rapidly precipitated in the form of sulphate, etc. 



Use of Dead- Sea Water. --M. Roux has laid before the French 

 Academy an analysis of this water, which shows that, in addition to 

 considerable quantities of chlorides of magnesium, sodium, calcium, and 

 potassium, it contains bromide of magnesium to the extent of 0.3G4 

 grammes in 100,000 grammes. M. Roux considers that it may prove 

 a very valuable medicine in scrofulous, syphilitic, and many other 



