IF. F. Hillebrand — Composition of Yttrialite. 147 



Finally, if the values for nitrogen and helium are really 

 anywhere near so great as given, an additional argument 

 against the validity of his formula is furnished. For, in the 

 light of Kohlschutter's recent researches* and my own less 

 conclusive work of a much earlier date,f it is in the highest 

 degree probable that nitrogen and helium are not occluded in 

 uraninite and other minerals but are in chemical combination. 

 Now, if this is so, in a mineral containing as much as 1*4 per cent 

 of nitrogen by weight this must, quite irrespective of its form 

 of combination, play so important a role in the molecule as to 

 utterly invalidate any formula based on calculations from 

 which it is omitted. If the above percentage is made up in 

 large part of helium, its effect, because of its low atomic 

 weight, must be vastly greater than that of nitrogen. 



Until light is thrown on the nature of the combinations these 

 two gases form in minerals, no very positive conclusions can be 

 reached as to the formulas to be assigned to those minerals 

 which contain them in more than traces. 



Chemical investigation of Yttrialite. 



At the earnest request of Mr. W. E. Hidden, the discoverer 

 of yttrialite, I undertook to reanalyze the mineral in order if 

 possible to settle definitely the question of its composition. 

 This seemed especially desirable since a large quantity of very 

 fine material was available. 



The appearance and behavior of the mineral agreed in all 

 respects except one with those of the original description. J It 

 is there stated that the strongly ignited mineral is insoluble in 

 acid. This is a mistake, for when powdered the solubility in 

 hydrochloric acid is even then perfect, although not rapid. 



Careful examination of thin sections under the microscope 

 showed a condition that augured ill for decisive analytical results 

 despite the apparently fine quality of the large specimens. 

 Distinctly foreign mineral fragments were as good as absent 

 except for insignificant coatings of a white alteration product, 

 presumably a carbonate, but considerable shading was apparent 

 in the slides, indicative of alteration or intimate contamination 

 in the mass of the mineral itself. However, after treatment 

 with hot dilute hydrochloric acid (whereby much yttrialite was 

 dissolved) followed by dilute sodium carbonate, the clear glassy 

 residue appeared to be improved in appearance and the specific 

 gravity of two samples, each composed of small grains uniform 

 in size for each sample, had risen from 4*596 and 4*590 to 4*654 



* Adh. der Chem., cccxvii, 158, 1901. 



f Bull. TJ. S. Geol. Surv., No. 78, pp. 76-78, 1891. 



% This Journal, xxxviii, 477, 1889. 



