40 SLATE DEPOSITS AND INDUSTRY OF UNITED STATES. 
analyses L, M, Q, R);« hence MgC0 3 is indicated as the next most important isomor- 
phons element of the carbonate. Analyses M, Q, and R, taken together in the order 
named, afford positive evidence that MnC0 3 is present either as an independent min- 
eral or as a component of the complex carbonate, for as C0 2 decreases from the green 
center through the purple rim to the outer red, so does MnO, and at such a rate that 
with no carbon dioxide MnO would likewise disappear. In general, too, those slates 
high in C0 2 show a relatively high MnO content. Analysis 201d (p. 71) shows also 
that manganese carbonate is found as a vein formation in the slates, and Professor 
Dale has found with the microscope some indications of its presence in the lenses of 
the red slate, at least. In order to be able to credit the fading to the carbonate, it is 
necessary still to show that it contains FeC0 3 as a constituent, for, while the man- 
ganese might produce discolorization by oxidizing, its amount is slight, and the color 
due to its oxidation products alone would be black rather than brown. Because of 
the above-mentioned ready solubility of the ferrous silicate or silicates in acids, 
chemical proof of the presence of ferrous carbonate is not obtainable, but from our 
general knowledge of its relations to those of magnesium and manganese it is in the 
highest degree probable that it does exist either as a distinct mineral or as a compos 
nentof the doloniilic carbonate, and, in fact, it would be somewhat surprising if, with 
magnesium and manganese present as carbonates, iron should be absent. The needed 
proof, however, is supplied by the microscope, as detailed in the text of Professor 
Dale's report (p. -105). 
If it is objected that some green slates comparatively rich in carl >onate fade less than 
others which are much poorer, it may be reasonably urged that the relative propor- 
tions of the several carbonates are doubtless subject to change in different slates, as^ 
in the natural order of things they must be, since the original composition of thes' 
slate-forming materials must have differed in each case. This being so, it follows that i 
a mere test as to the relative amount of C0. 2 can furnish no guide in advance as to thee 
fading qualities of a slate, as might be the case were the composition of the mixed! 
carbonates always constant. 
While pyrite is never a visible constituent of the red slates, there seems no other 
way to account for the sulphur found, since careful tests failed by far to show an 
equivalent amount of S0 3 . Hence in the analysis pyrite is reported in all cases. 
The phenomenal percentage of barium in 201e (K), as compared with other slates, 
has been of service as showing that, in this case at least, it is mainly, if not alto- 
gether, a constituent of some silicate, or silicates, and not of barite only, which latter r 
mineral, according to Professor Dale, has been observed on joint planes and in crys- 
talline concretions, for the sulphur is totally inadequate to form barite in this case. 
The condition of the nickel and cobalt has not been definitely ascertained. From 
the analysis of the manganese carbonate 201d it might appear as if they were con- 
stituents of the carbonate in the slates, but it is not impossible that they may be in 
combination with arsenic, or arsenic and sulphur, as arsenides and sulpharsenides, 
even if the presence of arsenic has not been revealed, no test having been made foi j 
that element. In all the tests made for nickel and cobalt, both elements were found. 
and in one case, probably a maximum, their combined percentage as oxides was 
0.025. 
Heating of the slates in tubes closed at one end gave without exception alkaline 
vapors and whitish sublimates, which latter reacted for.S0 3 , CI, and strongly for NII 3 
In eight cases the amount of ammonia thus given off in both conditions was ascer 
tained by nesslerization and found to range from 0.0075 per cent in the case of 760( 
(H) to 0.04 per cent for 305c? (P). This last is a black slate carrying nearly 0.5 pei 
cent of carbon, but the ammonia obtained was not sensibly higher than in some o 
the green slates, as 645a (F) with 0.035 per cent NH 3 , or 314 of '95 (I), with 0.0! 
per cent NH 3 . 
a See pp. 16, 73. 
