hillebrand.] IMPORTANCE OF THOROUGH ANALYSES. 1 5 
often trying problem. Although long practice may have enabled 
one to do certain parts of it almost mechanically, one is still from time 
to time confronted with perplexing questions which require trained 
judgment to properly meet and answer, and there 1 is still room for 
important work in some of the supposedly simplest quantitative deter- 
minations. If the results are to have any decided value for purposes 
of scientific interpretation and comparison, thc} T should be the product 
of one competent to find his way through the intricacies of an analysis 
in which from fifteen to twenty-five different components are to be 
separated and estimated with close approach to accuracy, and this a 
beginner can not hope to do in the majority of cases. The conscien- 
tious chemist should have a live interest in this matter. He should 
work with a twofold purpose in view — that of lightening the labors of 
those who come after him by enabling them to use his work with less 
supplementary examination and of thereby enhancing his own reputa- 
tion by meriting encomiums on work that has stood the test of time. 
The petrographer, again, should seek to have his analyses made as 
complete as possible, and not, as is so often the case, be content with 
determinations of silica, alumina, the oxides of iron, lime, magnesia, 
the alkalies, and water. The latter, it is true, are entirely justifiable 
at times, and may serve the immediate purpose for which they were 
intended, but their incompleteness may, on the other hand, not only 
conceal points fruitful of suggestion to the attentive mind, but, what is 
of still greater importance, they may be actually misleading. Enough 
instances of totally inaccurate conclusions to be drawn from them have 
fallen under my own observation to fully justify this plea in favor of 
greater completeness in rock and mineral analyses made for purely 
scientific purposes. 
The importance of the points indicated in the foregoing paragraph 
is shown by the difference between the analyses given on the following 
page. The specimens were taken and analyzed at widely separated times 
and hy different persons, it is true, but they were unquestionably from 
the same rock mass, in which, however much the relative proportions 
of the different mineral constituents might vary within certain limits, 
there can be no reason to doubt the general distribution of all the 
elements shown by the second analysis. 
