Chemistry and Physics. 373 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. The Action of Ozone upon Metallic Siloer and Mercury. — 

 The blackening of bright silver by ozone is generally given as one 

 of its characteristic reactions, particularly in distinguishing it 

 from hydrogen peroxide. It would seem, therefore, that the 

 reaction should take place easily under any conditions. However, 

 Manchot and Kampschulte have found that when a piece of 

 silver is held at the mouth of a Siemens' ozone tube, there is 

 little blackening when the ozone is dry, and even when the silver 

 is moistened the reaction is uncertain and not characteristic. 

 They have found, on the other hand, that if the silver is heated 

 to near redness and then is exposed to ozone as it cools, a beautiful 

 coating is quickly obtained, but the reaction becomes indistinct 

 when the metal has cooled to a temperature still considerably 

 above that of the room. By a series of experiments at known 

 temperatures it was shown that the reaction with very dilute 

 ozone is scarcely appreciable at 100°, but becomes more distinct 

 as the temperature rises, until it becomes best and very beautiful 

 at 220-240°. The intensity of the reaction decreases gradually at 

 still higher temperatures, on account of the decomposition by 

 heat of the silver oxide, and it does not occur at all at 450°. 

 The experiments just described were carried out with carefully 

 dried gas, but it was found that moist ozone gives the same 

 results. The handbooks of chemistry say, on the contrary, that 

 completely dry ozone does not oxidize dry silver. The interest- 

 ing fact was observed that a great number of substances adher- 

 ing to the surface of silver, even in exceedingly minute quantity, 

 impart to it the property of being instantly blackened by ozone, 

 even in the cold. For instance, silver polished with emery paper, 

 or etched with nitric acid and carefully washed and dried, shows 

 this property. Many metallic oxides give this catalytic effect. 

 Curiously enough, certain silver surfaces which were susceptible 

 to the action of ozone in the cold lost this property after stand- 

 ing for some time at ordinary temperature. In the case of mer- 

 cury it was found that the temperature of greatest action of 

 ozone is 1*70°. Similarly to silver, the action is gradually less 

 below and above this temperature. — Berichte, xl, 2891. 



H. L. W. 



2. The Separation of Tellurium from the Heavy Metals. — 

 Brauner and Kuzma have made a useful contribution to the 

 analytical chemistry of tellurium. They find that when this ele- 

 ment is precipitated in the customary manner by means of sul- 

 phur dioxide, other metals, such as mercury, lead, bismuth, 

 copper, cadmium, arsenic, antimony, and thallium, tend to come 



