20 SOME PRINCIPLES AND METHODS OF ROCK ANALYSIS, [hull. 176. 
in Denver may oe useful to most chemists interested in mineral and 
especially rock analysis. 
The original publication of these data in Bulletin No. 148 was 
primarily intended to show the principles and methods according to 
which the major part of the very many hundreds of analyses therein 
brought together had been executed, and thus to furnish a partial 
measure of the trustworthiness of those analyses, rather than to serve 
as a practical manual of rock analysis. But the use which has been 
made by mineral chemists of that bulletin has seemed to render it 
advisable to amplify somewhat in detail and to add, besides a few new 
methods, a number of alternative ones which are known or believed 
to be good, in order that those who may wish to use this treatise as a 
practical guide shall have a choice from which to select in case the 
rather expensive apparatus or complicated arrangements sometimes 
preferred are not available. Where silicate analyses are very fre- 
quently made, however, it is a saving of time and of money in the end 
to set up permanent arrangements for convenience in estimating 
water, carbon dioxide, ferrous iron, making reductions in hydrogen, etc. 
Stress will be laid on those points meriting particular attention, and 
now and then a brief discussion or criticism of methods elsewhere in 
vogue may be entered into. 
In the earlier years of the existence of the Washington laboratory 
opportunity was afforded for the testing of novel methods and the 
devising of new ones, with most excellent results, as shown especially 
by the methods for separation of titanium, of lithium, and of boron, 
due to Prof. F. A. Gooch, to whose inventive skill chemists owe like- 
wise the perforated filtering crucible and the tubulated platinum cru- 
cible arrangement for the estimation of water. Of late years the press 
of routine work has been such as to more fully fill up the time of the 
much-reduced chemical force, and as a consequence it has been found 
impossible to subject to critical trial several separation methods of 
recent origin, some of which seem to be full of promise, or to follow 
out certain lines of investigation which have been suggested by the 
observations made in this laboratory. This, then, must be offered in 
explanation if, in the following discussion, it may seem to some that 
any of the methods followed are too conservative. In general the 
discussion will be confined strictly to such separations as may be 
required in the analysis of an igneous, metamorphic, or sedimentary 
silicate rock of complex mineralogical composition, in which the 
majority and possibly all of the ingredients in the list given below 
may occur in weighable or readily discoverable quantities: 
Si0 2 , Ti0 2 , Zr0 2 , A1 2 3 , Fe 2 3 , Cr 2 3 , V 2 3 , FeO, MnO, NiO, 
CoO, MgO, CaO, SrO, BaO, ZnO, CuO, K 2 0, Na 2 0, Li 2 0, H 2 0. 
P 2 5 , S, 1 S0 3 C, 2 C0 2 , Fl, CI, N. 
The special problems often arising in the analysis of rocks of extra- 
1 Usually as pyrite, not infrequently as pyrrhotite. 2 As graphite or coaly matter. 
