W. P. Headden — Some Phosphorescent Calcites. 307 



to be phosphorescent after insolation. Analysis shows that 

 the rare earths are present in such pieces, but in less than one 

 fifth of the maximum quantity found in other samples, while 

 the zinc oxide was a little more than one half the amount 

 found in the best material. 



We are dealing; with such small quantities and it is so diffi- 

 cult to select samples of 500 or even 50 grams that shall be 

 uniform in their contents of these elements, that we should be 

 careful to duly consider the possibility of variation in the 

 samples selected, and further, the probability of error, for it 

 is a delicate task to determine such small quantities of these 

 elements. 



If the question is one of chemical composition, it is evident 

 that we are compelled to consider the unusual things, those 

 which in this case are present in minute quantities, as impart- 

 ing this remarkable property. If this view be correct, the 

 common accidental constituents of calcite such as ferrous, 

 ferric, manganous, magnesic and probably zinc oxide are 

 eliminated from our consideration. 



In describing this calcite I have mentioned purple as a rather 

 common color in these samples or rather in portions of them. 

 This is seemingly an insignificant fact, especially if we assume, 

 as is usually done, that the pink, violet and purple is due to 

 some manganese compound. The purple due to manganese, 

 particularly as permanganate, gives a characteristic absorption 

 spectrum ; accordingly the purple portions of the cleavage 

 pieces were examined with aid of the spectroscope. The light 

 from an incandescent lamp gives an excellent continuous spec- 

 trum when viewed through the yellow or the colorless calcite, 

 but a pronounced black line appears whenever a purple portion 

 passes between the lamp and the slit of the spectroscope. If 

 the purple color is intense enough two lines appear. JSTo sample 

 examined failed to give the stronger of these two lines very 

 satisfactorily indeed. These two lines coincide with the a and 

 /3 lines of didymia, which fact was ascertained by using a 

 solution containing didymia, when the lines produced by the 

 purple portions of the calcite were found to be coincident with 

 the a and /3 lines of the solution and are, therefore, probably 

 due to this earth. 



The analytical results justify the inference that the yttrium 

 group has a greater influence upon the phosphorescence of 

 the calcite than the cerium group ; and this inference is greatly 

 strengthened by the spectroscopic proof that the didymia 

 can readily be detected in portions of the crystals which have 

 not, under any conditions, been observed to phosphoresce. 

 As cerium, lanthanum and samarium are usually if not always 

 associated with didymia, one is justified in assuming that the 



