abstracts: geology 631 



method permits the use of potassium dichromate with its numerous 

 advantages. (2) The reduction of the solution with electrometric con- 

 trol eliminates the removal of excess reducing agent, which must be done 

 with the usual methods of reduction. (3) Conditions, such as acidity, 

 need not be controlled, except within very wide limits, and hydro- 

 chloric, sulfuric, or hydrofluoric acid, or mixtures of these, may all 

 be used. In contrast to these wide limits, compare the narrow acid 

 limits (1.5 to 2.5 per cent by volume of H2SO4) within which the re- 

 duction with SO2 or H2S must be carried out and the precautions which 

 must be taken in a permanganate titration in the presence of either 

 chlorides or fluorides. (4) The sensitivity and accuracy of the method 

 make possible (a) the determination of a few tenths of a milligram of 

 tin, chromium, ferrous or ferric iron, and probably many other elements, 

 in the presence of large quantities of some other element, and (b) the 

 determination of blanks involved in some of the ordinary determinations 

 by reducing or oxidizing agents. (5) The time within which a determi- 

 nation can be carried out is greatly shortened. The content of ferrous 

 and ferric iron in a silicate, for instance, can be determined in from 

 15 to 30 minutes. (6) The precision attainable is comparable to the 

 best of the ordinary volumetric determinations. J. C. H. 



ANALYTICAI, CHEMISTRY.— E/^c/nca/ apparatus for use in electro- 

 metric titration. Howard S. Roberts. Journ. Amer. Chem. 

 Soc. 41: 1358-1362. September, 1919. 

 A description of simplified and inexpensive apparatus for use in the 

 titration of salts by the electrometric method. The potentiometer 

 consists of a sliding rheostat with attached scale. Several forms of 

 galvanometer may be used. H. S. R. 



GEOLOGY. — Upper Cretaceous floras of the eastern gulf region in 

 Tennessee, Mississippi, Alabama and Georgia. Edward Wilber 

 Berry. U. S. Geol. Survey, Prof. Paper 112: 7-172. pis. 33, 

 figs. 12. 1919. 

 Besides describing the floras, the author discusses in detail the dis- 

 tribution, lithologic character, stratigraphic relations, and local sec- 

 tions of the Tuscaloosa, Eutaw, and Ripley formations, and Selma 

 chalk. As the bulk of the flora is from the Tuscaloosa formation and 

 the representation of the Eutaw and Ripley floras is too meager to 

 throw any considerable light upon their correlation or the physical 

 conditions accompanying deposition, this contribution is devoted prin- 



