156 Scientific Intelligence. 



serves as the anode, alloys of beryllium may be obtained. — C. H., 

 cxxvi, 744-746, March, 1898. G. f. b. 



4. On Colloidal Silver. — Some experiments have been made by 

 Lottermoser and yon Meter on the action of various reagents 

 on colloidal silver. They find that acids precipitate it from solu- 

 tion in the "molecular" state, time and dilution being of great 

 importance. To study the influence of time on the change from 

 the colloidal to the molecular condition, a known amount of acid 

 was added to the colloidal solution and the time was observed 

 which was required for the complete change. By placing a drop 

 of the solution on a glass plate resting on white paper, the end of 

 the reaction is easily detected ; the time being noted as soon as 

 the separation of fine silver particles can be readily seen. The 

 results of the experiments are given in a table. They show that 

 the less the amount of acid used the longer the time required for 

 the reaction. Moreover, the amount of acid required to produce 

 the change in a given time appears to be inversely as the concen- 

 tration of the solution. As to the precipitation of colloidal silver 

 by salts of the heavy metals, experiment shows that where reduci- 

 ble metallic chlorides are used there is formed silver chloride and 

 a lower chloride of the metal ; a portion of the silver, however, 

 being always precipitated in the insoluble form. If the solution 

 of colloidal silver and of the metallic chloride are both very 

 dilute, it frequently happens that neither silver chloride nor the 

 lower metallic chloride is precipitated, both remaining in solution 

 in the colloidal form. This behavior is particularly shown by 

 mercuric chloride. Neither the chloride, bromide or iodide of 

 colloidal silver appears to have any application in photography, 

 though the iodide is of interest therapeutically. —J. pr. Ch., II, 

 lvi, 241, 1897; lvii, 540, July, 1898. g. f. b. 



5. On Silver peroxide and peroxynitrate. — In continuing his 

 researches on the higher oxide of silver and its compounds 

 Mulder has observed that when the substance Ag 7 NO n is de- 

 prived of an atom of oxygen and the residue is extracted with 

 water, silver nitrate goes into solution and silver peroxide Ag 2 2 

 remains. Since the silver nitrate can be extracted in a short 

 time, the nitrate Ag 7 NO n may be regarded as having the compo- 

 sition (Ag 2 2 ) 3 . AgN0 5 . When boiled with water the peroxy- 

 nitrate is decomposed, oxygen is set free and silver nitrate goes 

 into solution, leaving a residue of silver peroxide. This suggests 

 a convenient method for preparing the peroxide. This higher 

 oxide dissolves in concentrated sulphuric and in concentrated nitric 

 acid, giving brown solutions. The presence of water accelerates 

 the decomposition of these solutions. The peroxide is not solu- 

 ble in acetic acid though when diluted silver acetate and oxygen 

 are formed. A method for determining the excess of oxygen in 

 the peroxynitrate is described, based on the decomposition of this 

 salt by water. When kept for some time the peroxynitrate un- 

 dergoes slow spontaneous decomposition even over sulphuric acid. 

 So slow is this change, however, that the author estimates that it 



