116 
CONTRIBUTIONS TO MINERALOGY. 
[BULL. 262. 
ine and hydroxy 1 are known to do. There is, then, no reason that the 
writer can see why the alumina, boric acid, and water in dumortierite 
should not be present in fixed quantities, and that the variations 
shown in analyses are not due to " isomorphous replacements," but to 
inaccuracy of analyses or impure material. 
Having- established the above formula from the analysis, let us see 
how closely the other analyses conform to it. 
The best series of analyses is that made Ity Ford of mineral from 
three American localities. His first analyses of the Arizona material 
are tabulated below. 
8i0 2 . 
AU> :! 
Fe 2 0. 
B 2 3 - 
H 9 0. 
l. 
30. 00 
63. 20 
.23 
5.47 
1.45 
2. 
29. 66 
63. 74 
.23 
5.06 
1 . 38 
29.91 
63.76 
Average. 
29. 86 
63. 56 
.23 
5. 26 
1.41 
100. 32 
The ratios calculated from the average analysis give 
Si0 2 6. 29 or 6X1. 05 
ALA 7.94 8X .99 
BA 96 IX .96 
H 2 1. 00 1X1. 00 
The agreement with the proposed formula is perfect. 
His second analysis, that of the California mineral, shows slight 
variations from the results obtained by the writer. The presence of 
titanium was not determined. His analysis is: 
SiG 2 . 
AIA 
FeA 
BA- 
H,0 . 
30. 58 
61.83 
.36 
5. 93 
2. 14 
100. 84 
Ratios. 
6. 17 or 6X1. 03" 
7.40 8X .93 
1.04 1X1.04 
1 . 45 1 X 1 ■ 45 
The ratios agree well with the new formula except for the water 
content. Remembering, however, that the amount of water present 
is very small and that a difference of 0.10 per cent, would make a 
large difference in the ratios; that Ford determined his water by ignit- 
ing the mineral with lime, thus not weighing the water directly; and 
that the writer obtained only 1.52 per cent on the same mineral from 
