870 



SCIENCE. 



[N. S. Vol. XV. No 387. 



The various papers presented, whetlier 

 offered to Section C or to the American Chem- 

 ical Society, will be classified, in so far as pos- 

 sible, nnder certain general topics, and in this 

 manner will be distributed among the sessions 

 throughout the week. 



Brief abstracts of all original papers to be 

 presented should be forwarded to the commit- 

 tee on program, W. A. Noyes, Terre Haute, 

 Ind., Chairman, as early as convenient, and 

 not later than June 10. Papers to be presented 

 at the meeting are not necessarily in the same 

 form as those prepared for publication. For 

 public presentation few details should be 

 given, and papers should consist chiefly of a 

 clear and reasonably concise statement of the 

 results which have been obtained and the con- 

 clusions reached. Abstracts should be accom- 

 panied with a statement of the time desired 

 for the presentation of the paper. Persons pre- 

 senting general addresses and reviews under 

 special arrangement with the committee need 

 furnish only a brief outline as an abstract. 



Albert 0. Hale, 

 Secretary of the American Chemical Society. 



Brookltw, N. Y. 



Francis C. Phillips, 

 Secretary of Section C of A. A. A. S. 



Allegheny, Pa. 



on pyrite and marcasite. 

 To THE Editor of Science : In your number 

 for November 1, 1901, abstract is given of an ex- 

 cellent paper by Dr. H. N. Stokes 'On Pyrite 

 and Marcasite,' published in full in Bulletin 

 No. 186, of the U. S. Geological Survey. The 

 new method here proposed for quantitative de- 

 termination of these minerals involves many 

 intricate precautions which have been care- 

 fully and thoroughly worked out. So that 

 although the process and apparatus seem to 

 call for rather difficult manipulation, the 

 method is likely to be very welcome to every 

 student of this subject. Proper criticism of 

 its details could only be justified by repetition 

 of the process. In the absence of this I am 

 entirely ready to accept its logical results, 

 viz., that in this chemical method we at last 

 possess a satisfactory means for discrimina- 

 tion of the two minerals and for approximate 



determination — to a degree of accuracy of 

 within 1 to 3 per cent, in Dr. Stokes's skilled 

 hands — of the amount of each in the generally 

 composite specimens of pyrites found in 

 nature. 



There are certain inferences, however, which 

 I cannot recognize as proved, in opposition to 

 views advanced many years ago in my paper 

 'On the Variation of Decomposition in the 

 Iron Pyrites; Its Cause, and Its Relation to 

 Density' {Annals of N. Y. Acad. Set., Vols. 

 III. and IV., 1887). 



1. Dr. Stokes maintains 'that the hypothesis 

 that most specimens of pyrite and marcasite, 

 even when well crystallized, are mixtiires of 

 the two, or paramorphs, is without founda- 

 tion.' Of the truth of that hypothesis, I 

 think, much confirmation is found in the 

 results obtained by this chemical method. 

 In my paper (loc. cit., pp. 179-180) it 

 was pointed out for the first time 'that, on 

 a fresh fracture, unaffected by alteration, the 

 true color of marcasite is invariably grayish 

 white, nearly tin-white'; while 'normal pyrite 

 has a pale brass-yellow color' (p. 213). These 

 color characteristics of the normal native 

 minerals are accepted by Dr. Stokes, but fur- 

 ther assumed by him as criteria for discrimi- 

 nation of the pure minerals, the very problem 

 under investigation. Thus, in the determina- 

 tion of the oxidation-coefficient, p, five sam- 

 ples of pyrite and nine of marcasite were 

 selected 'as being free from visible impurity 

 and showing characteristic crystallization.' 

 These fourteen samples served as the stand- 

 ards on which all following determinations of 

 this coefficient have been based; apparently the 

 same criteria were assumed in selection of the 

 samples ground up for mixtures, in applica- 

 tion of the process to calculation of the curve. 

 But the visibility of impurities may have 

 little value in their recognition, above all 

 when the admixture becomes molecular. Even 

 those samples, at the one extreme, selected for 

 purity and mostly for perfection of crystal- 

 lization, have revealed to Dr. Stokes, in the 

 variations of p, the intermixture of one or of 

 the other mineral, as well as of other impuri- 

 ties, in notable amount. At the other extreme 

 (page 36 of his paper), out of 13 miscellaneous 



