hllebram)] COMPOSITION OF YTTRIALITE. 63 
£"R'" 6 Si 6 22 , which is susceptible of a variety of interpretations. It 
nay represent a basic salt of diorthosilicic acid R"R"' 5 (R"'0)'(Si 2 7 ) 3 
>r of metasilicic acid R / 'R" , 8 (R"'0)' 4 (Si0 8 ) 6 , or possibly even of other 
icids. 
Finally, if the values for nitrogen and helium arc 4 really anywhere 
iear so great as given, an additional argument against the validity of 
lis formula is furnished. For in the light of Kohlschutter's recent 
researches'* and my own less conclusive work of a much earlier date, 6 
t is in the highest degree probable that nitrogen and helium are not 
occluded in uraninite and other minerals, but are in chemical combina- 
tion. Now, if this is so, in a mineral containing as much as 1.4 per 
lent of nitrogen by weight, this must, quite irrespective of its form of 
combination, play so important a role in the molecule as to utterly 
nvalidate any formula based on calculations from which it is omitted. 
[f 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 
iitrogen. 
Until light is thrown on the nature of the combinations these two 
?ases form in minerals, no very positive conclusions can be reached as 
the formulas to be assigned to those minerals which contain them in 
nore than traces. 
CHEMICAL INVESTIGATION OF YTTRIALITE. 
At the earnest request of Mr. W. E. Hidden, the discoverer of 
ttrialite, I undertook to reanalyze the mineral in order if possible to 
fettle definitely the question of its composition. This seemed espe- 
ially desirable since a large quantity of very line material was 
[vailable. 
The appearance and behavior of the mineral agreed in all respects 
xcept one with those of the original description/ It is there stated 
dat the strongly ignited mineral is insoluble in acid. This is a mis- 
ike, for when powdered its solubility in hydrochloric acid is even 
en perfect, although not rapid. 
Careful examination of thin sections under the microscope showed a 
'jmdition that augured ill for decisive analytical results despite the 
parently tine quality of the large specimens. Distinctly foreign 
ineral fragments were as good as absent except for insignificant 
>atings of a white alteration product, presumably a carbonate, but 
tasiderable shading was apparent in the slides, indicative 1 of alter- 
"lion or intimate contamination in the mass of the mineral itself. 
1 pwever, after treatment with hot dilute hydrochloric acid (whereby 
ich y ttrialite was dissolved) followed by dilute sodium carbonate, tin 1 
"Ann. derChem., 317, 1901, p. L58. 
6 Bull. U. S. Geol. Survey No. 78, 1891, pp. 76 78. 
cAa Jour. Sci., ser. 3, vol, 38, 1889, p, 477. 
