292 CARNEGIE INSTITUTION OF WASHINGTON. 



the reaction Sb(s)+H20+3© =SbO+ + 2H+ was computed to be -0.212± 

 0.002 volts. These are the first experimental results that afford even an 

 approximate measure of the antimony potential. The value obtained places 

 it between hydrogen (±0.0 volt) and bismuth ( — 0.30 volt) in the potential 

 series, showing it to be more reducing than the latter element. In inter- 

 preting these results it was necessary to know the activity of the hydrogen-ion 

 in the perchloric-acid solutions. This was determined by comparing the 

 activity of this acid with the known activities of hydrochloric acid by measur- 

 ing the electromotive force of cells of the type H2 (1 atm.), HCIO4 (at c), 

 HCl (at c), H2 (1 atm.). For values of the concentration c between 0.1 

 and 1.1 normal such cells were found to have electromotive forces of only a 

 few tenths of a millivolt. As this may well arise only from the liquid poten- 

 tial due to the difference in mobilities of the two anions, the conclusion is justi- 

 fied that the two acids have the same activity-coefficient at the same con- 

 centration. 



All these results have been written up and sent to the Journal of the Amer- 

 ican Chemical Society for publication. 



The line of research referred to in last year's report on the determination 

 of the free energy of water-soluble compounds by measuring the electro- 

 motive force of cells containing them in contact with organic liquids has 

 been continued by Mr. C. H. Prescott jr. Thus the free energy of solid 

 sodium chloride has been derived from the electromotive force at 25° of 

 the cell. 



Na in Hg, NaCl(s) under CsHn OH, HgCl(s)+Hg(l). 

 The value has thus been found to be —90,800 calories, in fair agreement with 

 the value —91,700 calories obtained by Allmand and Polack from measure- 

 ments with aqueous solutions. 



3. A System of Qualitative Analysis including the Rare Elements. 

 During the past year, with the assistance of W. C. Bray and E. H. Swift, 



the work on the system of qualitative analysis, including all the metallic 

 elements, has been continued. The plan of separation and detection of the 

 elements of the groups precipitated by ammonium hydroxide and sulfide has 

 been perfected and brought into form for publication. The rare elements 

 gallium and indium have now been included in the scheme. As special items 

 of analytical and preparative importance may be mentioned the discoveries 

 that gallium, heretofore separated from associated elements with much diffi- 

 culty, can be separated in a single operation from all of them except iron, by 

 extracting it from a solution 6-normal in hydrochloric acid with ether; and 

 that indium can be separated from rare-earths and other elements by pre- 

 cipitating it as the very characteristic bright-yellow sulfide from a 6-normal 

 acetic-acid solution. 



4. The Structure of Crystalline Substances determined by X-Rays. 

 The researches on the determination of the arrangement of atoms in the 



crystals of typical inorganic substances have been continued. Dr. R. G, 

 Dickinson has worked out a structure for stannic iodide (Snl4), which ac- 

 counts satisfactorily for the X-ray data; this being the first inorganic sub- 

 stance which has been found to have a distinctly molecular structure. Dr. 

 R. M. Bozorth has investigated the cubic crystals of arsenic trioxide and 

 antimony trioxide, and has found them also to show molecular segregation, 



