P. T. Walden — Double Chlorides and Bromides, etc. 285 



This investigation furnishes another striking example of the 

 fact, already noticed several times in this laboratory, that caesium 

 halides form more complete series of double salts than the 

 halides of the other alkali-metals. With caesium chloride we 

 get a complete series, while with the chlorides of the other 

 alkali-metals only one type appears. In the bromides no double 

 ferric potassium salt could be isolated, whereas two well- 

 defined and comparatively stable compounds were obtained 

 with caesium. 



"Wells and Campbell* have called attention to the fact, that, 

 in a number of cases, double halides show an increase in ease 

 of formation from the iodides to the chlorides. No better 

 illustration could be had of this truth than the series of salts 

 prepared in the present investigation, where the chlorides were 

 made in greater number and with more ease than the bromides 

 while no iodides at all could be obtained. 



Preparation. — All these salts were made by mixing solu- 

 tions of the simple halides, evaporating and cooling to crystal- 

 lization. It was found necessary in all cases to use solutions 

 slightl}" acidified with the corresponding halogen acid, in order 

 to prevent the formation of basic salts. A record, as nearly 

 exact as possible, was kept of the relative quantities of the 

 constituents used and this has been indicated under each salt. 

 The crystals were freed from the mother liquor by pressing 

 between smooth filter papers, and in every case where it was 

 admissible they were further dried by exposure to the air of 

 the laboratory. Where the salt was at all deliquescent it was 

 at once removed to a tightly stoppered tube whose weight had 

 been previously determined and weighed without loss of time. 

 In this manner a quite unstable body could be analyzed and 

 satisfactory results obtained. The purity of all the simple 

 alkali-halides was tested with the spectroscope before using. 

 The very pure rubidium chloride used for this work was furn- 

 ished to this laboratory for the encouragement of scientific 

 investigation by Herr E. Merck of Darmstadt, through his 

 agents, Messrs. Merck & Co. of New York, and our thanks are 

 due to him for his unsolicited generosity. 



Method of analysis. — Iron was weighed as Fe.,0 3 in all 

 cases, after having been separated from the alkali-metal by 

 precipitation with ammonia. The filtrate from this precipita- 

 tion was evaporated to dryness, the alkali-metal converted into 

 sulphate and weighed as such after ignition in a stream of air 

 containing ammonia. Ammonium was estimated by distilling 

 with a solution of potassium hydroxide, absorbing the NH 3 

 liberated in hydrochloric acid and determining its amount by 



* This Journal, III, xlvi, 432. 



