396 Scientific Intelligence. 



In both herderite and topaz an increase in hydroxyl is 

 accompanied by a decrease in specific gravity and an increase 

 in the indices of refraction. In monoclinic herderite the axes 

 of greatest and least elasticities correspond nearly to the crys- 

 tallographic axes, and overlooking this slight deviation the 

 optical orientation in both minerals is the same, a = a, b = h 

 and c = c. Since topaz is positive and herderite negative the 

 acute bisectrices are c and a respectively, but the angle of the 

 optical axes measured in each mineral over the axis of least 

 elasticity (that is in herderite over the obtuse bisectrix) is 

 smaller for the hydroxyl than for the fluorine compound. In 

 both minerals the substitution of hydroxyl for fluorine causes 

 a change in the lengths of the crystallographic axes but the 

 changes are not of the same character, since in herderite the a 

 and c axes both increase while with topaz a increases and c 

 decreases. 



Laboratory of Mineralogy and Petrography, 



Sheffield Scientific School, April, 1894. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. On the Effect of absorbed Hydrogen on the Electrical Prop- 

 erties of Palladium. — In a recent paper by Brtjcchietti, he gives 

 the results of his investigations upon the effect of the absorption 

 of hydrogen upon the thermo-electric power and the electric resist- 

 ance of palladium. He finds that this absorption increases the 

 resistance, the increase being proportional to the quantity ab- 

 sorbed ; a palladium wire saturated with hydrogen having a 

 resistance 1*55 times as great as before it was charged. When 

 the same wire is repeatedly saturated with hydrogen and dis- 

 charged, its resistance appears to tend toward a constant value 

 (whether hydrogen is present or not) ; this value being intermed- 

 iate between its resistance before being charged and that after 

 being charged for the first time. In his experiments on thermo- 

 electric power, the author used a couple consisting of palladium 

 and nickel and found that the power of this couple increases with 

 the amount of hydrogen which the palladium has absorbed; so 

 that when the metal is saturated, the thermo-electric power is 

 1*66 times that observed before charging. When a thermo- 

 electric couple was made of charged and uncharged palladium, 

 the current at the cooler junction was found to flow from the 

 charged to the uncharged metal. — Nciture, xlix, 65, November, 

 1893. G. F. B. 



2. On the Determination of the Molecular Formidas of 

 Liquids by means of their Molecular Surface Energy. — The 



