236 Scientific, Intelligence. 



3. On the Solution of Platinum and Gold in Electrolytes. — It 

 has been observed by Margtteles that if an electro-magnet pro- 

 vided with a vibrating armature be made to act as a contact 

 breaker to the current from two Daniell cells, an electrolytic cell 

 provided with platinum or gold electrodes being included in the 

 circuit, the metal can be made to dissolve in hydrochloric, nitric 

 or sulphuric acid, or in potassium or sodium hydrate. The solu- 

 tion always takes place from that electrode which is for the time 

 being the anode. It is helped in some way, however, by the dis- 

 charge current from the magnet, as the current from the battery 

 alone does not effect the solution, neither when continuous nor 

 intermittent. — Wied. Ann., lxv, 629-634, June, 1898. G. f. b. 



4. Aqueous Solutions of Metallic Gold. — By treating a feebly 

 alkaline boiling solution of gold chloride with a reducing agent, 

 Zsigmondy has shown that a red aqueous solution of metallic 

 gold may be obtained.* Formaldehyde seems to be the best 

 reducing agent, less satisfactory results being given by acetalde- 

 hyde, alcohol and hydroxylamine. Sometimes the solution, in- 

 stead of being red, is dark purple, violet or bluish black and 

 appears turbid. The solutions of gold are very dilute, only about 

 0-005 gram of gold to the hundred cubic centimeters. They 

 undergo no change when boiled until reduced to less than half 

 their volume, when they become violet-black and deposit gold as 

 a black powder. The solutions may be concentrated by dialysis, 

 which become intensely red and contain 12 per cent of colloidal 

 gold. Solutions of neutral salts and mineral acids change the 

 color to blue and slowly precipitate finely divided metallic gold. 

 Potassium ferrocyanide produces a green coloration, subsequently 

 becoming yellow. Acetic acid gives a violet red and finally a 

 black. Alkalies precipitate blue gold. Alcohol in excess changes 

 the color gradually to dark violet, precipitating the metal com- 

 pletely in a condition in which it is soluble in water. When sub- 

 mitted to the action of a current, aqueous solutions of gold act 

 like other colloids; the metal travels toward the cathode, but 

 does not penetrate the membrane. — Liebif s Annalen, ccci, 29-54, 

 June, 1898. G. f. b. 



5. On the Explosion of Mixtures of Methane and Air by the 

 Electric Current. — Extended experiments have been made by 

 Couriot and Meunier on the action first of incandescent wires 

 and second of electric sparks, on mixtures of methane with air in 

 various proportions, the gas being sometimes at rest and some- 

 times in motion. A mixture of 80 per cent of methane and 20 

 per cent of air, in motion, could not be fired by an incandescent 

 wire nor even by the spark at the break when the wire fused ; 

 though it readily ignited in contact with a flame. If an electric 

 current produces any effect at all on a mixture of methane r.hd 

 air, the only effect is an explosion. But under no circumstancas 

 were the authors able to produce an explosion with an incandes- 

 cent wire. Whenever an explosion was produced it was due to 

 the spark produced at the breaking of the wire. A mixture con- 



* See Faraday's Exp. Res in Chem. and Phys., p. 411. 





