132 
The composition of related minerals is shown in columns 
II to V. 
According to Rutherford and Boltwood’s value for the ratio 
of radium to uranium in such minerals, Pilbarite would contain 
about 7.5 centigrams of radium per ton, according to Mme. 
Gleditsch s+ values, probably somewhat less, being a weathered 
compound. 
In calculating a formula for Pilbarite, the whole of the 
tantalic oxide and the requisite, amount of manganese and iron 
oxides to form tantalite are rejected, there being abundant 
evidence in support of this. The traces of alumina and alkalis 
are also neglected as being certainly present as inclusions of 
mica and felspar. I he phosphoric oxide is probably present as 
monazite or xenotime. The essential constituents are evidently — 
UO, 
Th 0 2 
(Pb. Ca. Mg )0 . . 
Si 0 2 
H, 0 + 
H, O- 
The formula for Pilbarite is 
.094 molecules 
.118 
• 092 
.202* * 
•231 
•195 
therefore — 
UO, . ThOj . PbO. 2 Si 0 2 . 2H_, O. +2H 2 0 . 
The only two minerals with a formula approaching this are— 
Thorogummite, UO, . 3TMU . 3SiO, . 6H 2 O ; and 
Mackintosh te, U 0 a . 3Th0 2 . 3Si0 2 . 3H, O. 
Both of these minerals crystallise in the tetragonal system. 
It is evident that in the presence of lead oxide as an important 
constituent and also in the relative proportions of uranium oxide, 
thoria, silica and water, Pilbarite differs essentially from these 
minerals. In crystalline form it also differs essentially and one 
is therefore justified in considering it a new species. 
Pilbarite dissolves readily in strong or slightly diluted 
hydrochloric acid, leaving a flocculent residue of silica. It is 
completelj - decomposed by nitric and sulphuric acid, either 
concentrated or moderately dilute, but with these acids in addi- 
tion to silica a bulky mass of difficultly soluble thorium and lead 
salts separates out. During decomposition with hydrochloric 
acid a fair number of gas bubbles were seen to be given off, which 
were at first taken to be carbonic acid, but in view of the pos- 
sibility of helium being present as the result of degradation of 
uranium special efforts were made to collect the gas free from air 
or other gaseous impurities and to examine it. ^ The apparatus 
used was simply made but quite effective for the measurement of 
the helium to One-fiftieth of a cubic centimetre. It consisted of 
a so-called micro-chemical gas bottle of 125 c.c. capacity. By 
t Chemical News, Vol. C,, p. 173. 
* Neglecting SiCh present as felspar. 
