Chemistry and Physics. 2 "17 



and is producing motor fuel on a small scale. If this process 

 should succeed in competing with gasoline from petroleum it 

 would be of great industrial importance. — Jour. Indus. Eng. 

 Chem., 14, 165. h. l. w. 



3. The Precipitation of Arsenic as Sulphide from Solutions 

 of Arsenates. — It has been found by J. H. Reedy that this pre- 

 cipitation is greatly hastened by the presence of a small quantity 

 of a soluble iodide in the acid solution. This catalytic effect is 

 doubtless due to the reduction of arsenic acid to arsenious acid or 

 chloride by hydriodic acid and the continuous conversion of the 

 iodine thus set free to hydriodic acid by the hydrogen sulphide. 



This observation has been made use of in connection with work 

 in qualitative analysis by adding one or two cubic centimeters of 

 normal ammonium iodide solution just before passing in hydro- 

 gen sulphide in the regular course of analysis. The complete 

 precipitation of pentavalent arsenic is thus facilitated, and the 

 chances are much lessened that the student will fail to detect 

 arsenic because of non-precipitation at this point. The apparent 

 complications that mercury and copper may be precipitated as 

 iodides are rectified by the digestion with ammonium porysul- 

 phide which changes the iodides into the higher sulphides. — 

 Jour. Amer. Chem. Soc, 43, 2419. h. l. w. 



4. Colorimetric Analysis; by F. D. Snell. 12mo, pp. 150. 

 New York, 1921 (D. Van Nostrand Company). — In this book an 

 attempt has been made to collect for ready reference all the color- 

 imetric methods which experience has shown to be practical. The 

 first three chapters deal very satisfactorily with a classification of 

 the methods, the apparatus used and the calculation of the 

 results ; then the processes are described individually, according 

 to the substances to be determined. The book is a useful one for 

 reference use by analytical chemists, and while it appears that 

 some of the methods are not described with sufficient clearness 

 and fulness of detail, it may be said that references to the litera- 

 ture are usually supplied. As an example of lack of detail in 

 the description of a process it may be pointed out that the direc- 

 tions given for the determination of small amounts of potassium, 

 involving the precipitation of the platinic chloride, would not 

 lead to a proper precipitation and collection of this salt, but of 

 course, an experienced analyst would known how to modify the 

 directions. h. l. w. 



5. Fluid Resistance. — The phenomena which occur in the 

 motion of a real fluid are so complicated that theory alone is 

 capable of dealing with none but the simplest cases, and progress 

 in practical applications, as for example in the law of resistance to 

 the motion of a body through a fluid, can only be made by careful 

 experimentation. The following is a report of a study by 

 C. Wieselsberger of the resistance experienced by a cylinder 



