206 



SCIENCE. 



[N. S. Vol. XIX. No. 475. 



the same time as when the sense of smell 

 was used for a detector. The rate of 

 propagation of the smell of ammonia was 

 not markedly different when this had to 

 pass along the same tube either horizontally 

 or vertically upward or vertically down- 

 ward. "With camphor, however, while the 

 rates horizontally and downward were 

 about the same, the speed upward was 

 about twice as great. The smell given to 

 iron and brass by rubbing these with the 

 fingers was also tried, but gave no definite 

 results. 



On the Theory of the Electrolytic Rectifier: 

 S. R. Cook, Case School of Applied 

 Science. 



When aluminum is the anode in an elec- 

 trolytic cell in which oxygen is set free 

 there is very quickly introduced into the 

 cell an exceedingly high apparent resist- 

 ance. If aluminum is made the kathode 

 and carbon or platinum the anode, the re- 

 sistance is normal and very low. The 

 anomalous action of this cell was noted by 

 Professor Tait in 1869, but the cell did not 

 attract attention until 1897, when Pollok 

 and Gratz showed that the cell could be 

 used to rectify an alternating current. 

 Since 1897 investigations on the electrolytic 

 rectifier have been published by Wilson 

 and Norden, Burgess and Hambuecher, 

 Taylor and Ingals, and Dr. Guthe. Bach 

 investigator set forth an independent 

 theory for the high resistance of the 

 aluminum anode. The object of this in- 

 vestigation was to determine the cause of 

 this anomalous action of the aluminum 

 anode, and it was found by a series of meas- 

 urements of the applied electromotive force 

 and the current, and also of the counter 

 electromotive force with the same current; 

 that the very high apparent resistance 

 could be accounted for on the theory that 

 it Avas due to the counter electromotive 

 force. The potentials were measured by 



methods that were independent of the re- 

 sistance, and curves were plotted showing 

 the direct and counter electromotive force 

 with current. When the electromotive 

 force is greater than a certain critical value 

 depending on the temperature the high re- 

 sistance breaks down. This was shown to 

 be due to the crystallization of the film 

 around the aluminum anode, which exposed 

 free metallic surfaces to the ions. It was 

 also shown by direct determinations that 

 free metallic aluminum conducted as 

 readily when anode as when kathode, and 

 the counter electromotive force was due to 

 charged ions that could not penetrate the 

 film formed on the aluminum. 



On the Position of Aluminum in the Voltaic 

 Series and the Use of Aluminum as a 

 Positive Element in a Primary Cell: S. 

 R. Cook, Case School of Applied Science. 

 Wheatstone in 1855, while determining 

 the position of aluminum in the voltaic 

 series, found that when immersed in a 

 dilute solution of potassium hydroxide 

 aluminum was negative to zinc and positive 

 to cadmium, tin, lead, copper, iron and 

 platinum ; and in a solution of dilute hydro- 

 chloric acid aluminum was negative to zinc 

 and positive to other elements. The ob- 

 ject of the research was to make quantita- 

 tive measurements on the difference of 

 potential between aluminum and the other 

 elements in different solutions. Measure- 

 ments were made in several alkaline solu- 

 tions, three acids and several salts. It was 

 found that the difference of potential did 

 not remain constant, but, in general, any 

 solution the negative ions of which would 

 attack the aluminum producing a soluble 

 compound, the potential was more constant 

 than in those solutions in which oxygen 

 was the negative ion forming with the 

 aluminum an insoluble compound. Meas- 

 urements were taken with zinc, cadmium, 

 tin, lead, copper, iron and platinum in solu- 



