PART II. METHODS. 
I INTRODUCTORY REMARKS. 
The order hereinafter followed in describing the various chemical 
separations has little relation to the affinities of the constituents of the 
rock, but those are grouped together which can be conveniently 
determined in the same portion of rock powder. Thus, in the main 
portion are usually determined Si0 2 , Ti0 3 , MnO, NiO, CaO, SrO, 
MgO, total iron, and the combined weight of all the following: AI 2 3 , 
Ti0 2 , P 2 O r ,, Zr0 2 , all iron as Fe 2 3 , and nearly if not quite all vanadium 
as V 2 5 , also perhaps rare earths if present. In a separate portion is 
estimated FeO, and also the total iron, as well as BaO, if these last are 
desired as checks. The alkalies need a portion for themselves. In 
another, Zr0 2 , BaO, and total sulphur are very conveniently determined. 
For V 2 3 and Cr 2 3 still another and usually much larger portion is to 
be used. Determinations of C0 2 , C, H 2 0, Fl, CI, are all best made in 
separate portions of substance, though various combinations are possi- 
ble, as C0 2 and H 2 0, C and H 2 0, or H 2 0, Fl, and CI. In fact, by a 
judicious selection and combination of methods a very satisfactory 
analysis can sometimes be made on 4 grams of material without 
omission of anything of importance, though the time consumed will 
be greater than if ample material is available. 
As an illustration of the advantage to be gained by a little judgment 
in the combination of methods, the case of sulphur, barium, and zirco- 
nium may serve. Many chemists never look for the second and third 
of these, but by following the procedure given on pages 71—76 very 
little more labor is expended in confirming their presence or absence 
than that of sulphur alone. 
With only occasional exceptions, nearly all the constituents men- 
tioned on page 20 can be estimated if present in portions of powder 
not exceeding 1 gram each in weight. 
This is a convenient weight to take for the main portion in which 
silica, alumina, etc., the alkaline earths, and magnesia are to be sought; 
but it should, in general, be a maximum, because if larger the precipi- 
tate of alumina, etc., is apt to be unwieldy. Its weight can not often 
be much reduced with safety if satisfactory determinations of man- 
ganese, nickel, and strontium are to be expected. For the alkali por- 
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