372 The American Geologist. December, 1900 
Pseudomesolite is a new zeolite occurring in the plagio- 
clasyte. In its chemical composition it is very similar to 
mesolite, — that is to say, it may be considered as formed by a 
mixture of scolecite and of mesotype (MysScT, according to 
the analysis made). 
It occurs in white, fibrous masses, transparent in thin sec- 
tion. Its optic properties differ not only from those of meso- 
lite, but also from those of scolecite and mesotype. In pseu- 
domesolite. for example, the optic plane is not perpendicular 
to the elongation as in mesolite; n^ makes an angle of about 
20" with the vertical axis, and constitutes the acute bisectrix 
of the very small optic angle. 
CoMPARATi\E Chemical Compositiox. Methods of 
Analysis. The rock analyses have all been carried out by the 
method of St, Claire Deville, always being made in duplicate, 
and averages taken. In case the results were not sufficiently 
concordant, a third partial analysis was resorted to by the 
hydrofluoric acid method. 
The titanium precipitations were invariably made by pro- 
longed boiling after fusion with acid potassium sulphate in a 
solution containing a little free sulphuric acid. The separation 
01' iron and alumina was accomplished by conducting a current 
of hydrogen and hydrochloric acid gases mixed over the pre- 
cipitates heated to redness in a platinum tube. The hydrogen 
gas is generated in the ordinary way (Zn -|- H2SO4), and con- 
ducted well below the surface of strong sulphuric acid in a 
vessel, above which a stoppered vessel is fastened containing 
pure hydrochloric acid.* The stopper is turned until the HCl 
drops very slowly (2-6 drops per minute) upon the sulphuric 
acid, which liberates pure dry HCl gas. The hydrogen, form- 
ing at the same time, and passing through the H2SOS serves 
to keep the latter well stirred. 
This arrangement has the following advantages over the 
ordinary alternating gas method which may be termed the 
Deville- Rivot method : 
1. It requires less heat applied to the precipitates, a dull 
red being ample, and perhaps more than enough. 
2. It decreases the chance of explosion of hydrogen and 
oxygen (from air not wholly expelled, or leakage), both on 
*This arrangement was suggested to the writer by M. Arsandaux, 
l)acteriologist in the laboratory of the prefecture of the Seine. 
