:brand.] COMPOSITION ()K 5TTTEIAL1TE. 
07 
here being a slight deficiency of oxygen atoms in each case for the 
radical Si.,() ; , which is increased by allowing for the CO., and P 2 5 . 
In so far then as the character of the acid radical is concerned the 
results of Mackintosh's analysis are fully confirmed, and there is 
ibsolutely no ground for accepting Benedicks's basic formula, which, 
is I have already shown (p. 62), is based on a palpable error. Hut 
;he ratios are not at all such as to lend themselves to ready resolution 
into isomorphous salts of the acid H 6 Si 2 7 . By doing quite unwar- 
ranted violence to the analytical data the above formulas might be 
reduced to 
R" R'" 6 R"" (Si 2 7 ) 4 
which can be readily represented structurally as a single complex 
molecule or as a mixture of molecules like 3R'" 2 Si 2 7 -|-R"R""Si 2 7 . 
In neither case, however, is the type of the rowdandite molecule 
approached, which requires an altogether different ratio of monoxide, 
Hioxide, and trioxide bases; nor, if the second be accepted, is it at all 
dear that the two molecules would be mineralogically equivalent — 
that is, isomorphous. 
An alternative hypothesis is to regard the mineral as a mixture 
ontaining the anhydrous thorite molecule. Proceeding on this 
issuinption and deducting all thorium and uranium and the proper 
imounts of silicon and oxygen, the crude empirical formulas become 
Mackintosh . R" 65 R'" 373 Si 438 1501 
Hillebrand _ R" 61 R'" 386 Si 447 1533 
vh'wli may be interpreted as basic salts of metasilicic acid: 
R" 65 R'" 185 (R'"0)' 187 (Si0 3 ) 438 
R" 61 R'" 194 (R'"0)' 1M (Si() :; ) Mi 
or R" R'" 3 (R'"0)' 3 (SiO s ) 7 
lis last being easily susceptible of symmetrical representation in 
•aphic form. 
On the whole, I prefer to leave the constitution of yttrialite unsettled 
itil further evidence can be gathered, either from analyses of allied 
inerals or from yttrialite itself of more certain purity than any that 
is yet been discovered. 
It must not be forgotten that the gases other than CO., contained in 
e mineral may be the cause of the inability to arrive at satisfactory 
nclusions in the case of this and all other minerals which contain 
em, as I have already pointed out on page 63. 
My excuse for such a lengthy publication on a matter still unsettled 
the desire to prevent general acquiescence in the grouping under one 
e of minerals which can by no means be regarded as proved to 
ong to that type, and to which yttrialite certainly does not belong. 
