84 Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. Periodic Phenomena connected with the Solution of Chro- 

 mium in Acids. — While experimenting upon the behavior of 

 metallic chromium with acids, W. Ostwald has found the action 

 to be sometimes periodical. The evolution of hydrogen is at 

 first slow, then it increases to a maximum, becomes slow again, 

 again increases, and so on. The length of the periods from one 

 maximum to the next is to a certain extent constant, as is also 

 the rapidity of increase and decrease of gas evolution. The 

 author was able to measure the rapidity of action by an appa- 

 ratus analogous to those used in physiological laboratories lor 

 measuring changes in blood-pressure. In this apparatus the gas 

 evolved in a flask was allowed to escape through a capillary tube, 

 so that periodic changes of pressure occurred in the flask as the 

 gas was formed more rapidly or more slowly than it escaped 

 from the capillary tube. The periodic change of pressure is not 

 due to a change in the solution, but to a change in the metal. 

 When two pieces of chromium were placed beside one another, 

 but without touching, in the same hydrochloric acid, the appa- 

 ratus recorded a curve which was equivalent to the summation of 

 two curves for single pieces. When the two pieces were placed 

 in contact, however, the curve had a form like that produced by 

 a single piece. This behavior is connected with the fact that 

 passive chromium (i. e. that which does not dissolve in acids) is 

 made active upon contact with active chromium, for in this appa- 

 ratus contact with the piece which at the moment is giving off 

 hydrogen more actively instantly causes the other to dissolve 

 more rapidly. Different pieces of chromium did not behave uni- 

 formly, but gave curves of different forms. It is interesting 

 to notice that only the chromium from a single fusion gave 

 this periodic behavior. It was found that the addition of certain 

 reducing agents, sometimes even in very small quantities had 

 a very marked effect upon the form of the curves by retarding 

 the action. The addition of a little potassium iodide has this 

 effect, while cyanides, sulphocyanides and formaldehyde give still 

 greater effects in the order in which they are mentioned. Other 

 reagents, such as nitric acid, the lower oxides of nitrogen and 

 bromic acid, accelerate the action, making the periods shorter. 

 Hydrogen peroxide has a retarding action, like the reducing 

 agents. Measurements of the electrical tension between the 

 metal and the liquid showed that the metal is *1 volt more 

 anodic while rapidly dissolving than while slow action is taking 

 place. The variations in tension form a curve similar to that 

 given by the pressure of hydrogen. 



In a subsequent communication Ostwald has described further 

 experiments upon this subject. He has succeeded in obtaining 



