406 CARNEGIE INSTITUTION OF WASHINGTON. 



is independent of the condition, as regards polarization, of the exciting 

 light; (3) the crystals are strongly dichroic, but the bands belonging 

 to a given constant-interval series have the same plane of polarization. 



In the case of uranyl nitrate an investigation has been made of the 

 effect of water of crystallization upon the fluorescence and absorption 

 spectra. This salt is well suited for such a study, since it can be made 

 in the form of crystals containing respectively 2 and 3 molecules of 

 water as well as in the more common form of the hexahydrate. The 

 spectra of the different hydrated crystals are found to differ wideh% 

 both as regards the position of the principal bands and as regards the 

 intervals between bands. 



The study of the electrical properties of oxides carried on during 

 the sunamer of 1913, and originally undertaken by Mr. A. A. Somer- 

 ville, was continued during the year by Mr. C. C. Bidwell. The oxides 

 thus far studied are those of cadmium, lead, and iron. When possible, 

 simultaneous determinations have been made of the Hall effect, 

 thermo-electric power, and electrical conductivity through a -wide 

 range of temperature. 



In the case of lead oxide (PbO) the thermo-electric power lines 

 indicate the existence of a, j8, and 7 modifications. The transforma- 

 tion temperatures are fairly definite and the changes are reversible. 

 When Pb02 was slowly heated in air the reduction to Pb304, which sets 

 in sharply at about 280° C, is accompanied by profound changes in 

 resistance and thermo-electric power, and at a temperature of about 

 550° C. a further reduction to PbO is made evident by marked changes 

 in the properties studied. A polarization e. m. f. of approximately 

 1.7 volts was observed in Pb02, and Pb304 was found to collect rapidly 

 at the anode. 



Both the non-magnetic iron oxide, Fe203, and the magnetic oxide, 

 Fe304, were found to show a transformation point at about 780° C. 

 The change is apparently related to the recalescence which takes place 

 in pure iron at this temperature. Both oxides of iron show a variation 

 of electrical resistance with temperature which is in close agreement 

 with the relation predicted by the theory proposed by Konigsberger. 



The effect of high and low temperature upon the absorption of 

 selenium glasses in the visible spectrum has been studied by Mr. K. 

 S. Gibson. These glasses transmit mainly the light of longer wave- 

 lengths. A rise in temperature produces a very marked decrease in 

 transmission of these longer wave-lengths in such a way as to cause a 

 shift in the boundary between the transmission and absorption regions, 

 which in these glasses is very sharp, toward the longer wave-lengths. 

 The results of this investigation will be published shortly. At present 

 Mr. Gibson is studying the effect of temperature change upon the ab- 

 sorption and fluorescence of the synthetic ruby. The sharpness of 

 the bands and the well-marked dichroism of these crystals, both as 



