34 
CONTRIBUTIONS TO CHEMISTRY AND MINERALOGY. 
[bull. 167. 
In these cases the low boric acid of the analyses and the uncertain- 
ties as to the significance of the water determinations account for the 
chief variations between observation and theory. There is another 
complication also, due lo the fact that alternative expressions are pos- 
sible between which it is very difficult to decide. In the tourmaline 
from Haddam Neck, Connecticut, analyzed by Penfield and Foote, a 
somewhat different commingling of molecules seems to be necessary, 
partly on account of the higher proportion of lime in the mineral 
and partly on account of the fluorine. This tourmaline also admits 
of various alternatives in formulation, but it agrees well with the 
molecular mixture— 
3. Al 5 (Si0 4 ) 6 (B0 2 ) 2 . B0 3 Ca . Fe 4 H 4 , 
10. Al 5 (Si0 4 ) (i (B0 2 ) 2 . B0 3 (A10H) . Al 2 Li 2 H 4 , 
1. Al 5 (Si0 4 ) (; (B0 2 ) 2 . B0 3 Ca . Al 3 NaH 2 , 
6. Al fl (Si0 4 )fi(B0. 2 ).2 . BOaNaH . Al 3 NaH 2 ; 
in which Ca is equivalent to a replacement of NaH. This mixture, 
with the group AlOH proportional to fluorine, gives a good compari- 
son between analysis and theory, thus: 
Si0 2 
B 2 3 
Ti0 2 
A1 2 3 
FeO. 
MnO 
MgO 
CaO. 
Na 2 
Li 2 
H 2 0. 
F ... 
Found. 
36.96 
11.00 
.03 
39.56 
2.14 
2.00 
.15 
1.28 
2.10 
1.64 
3.10 
1.13 
Reduced. Calculated. 
101. 09 
36.75 
10.94 
39.35 
4.35 
1.27 
2.09 
1.63 
3.62 
100. 00 
36.86 
10.74 
39.44 
4.43 
1.15 
2.07 
1.54 
3.77 
100. 00 
The theoretical amount of fluorine needed to replace hydroxyl in the 
assumed group, AlOH, is 0.97 per cent/ Altogether, the comparison is 
fairly satisfactory. 
One analysis by Riggs, that of the magnesium tourmaline from 
Hamburg, New Jersey, I have omitted from my discussion. In that 
tourmaline there are variations which I can not readily account for. 
unless by assuming the presence in it of a molecule 
Al 5 (Si0 4 ) 6 (B0 2 ), . BO,R' 2 . R" 6 . 
Such a molecule, written structurally, exhibits affinities to garnet 
rather than to the micas; and I prefer to await further evidence before 
