[archibald-kern] solubilities OF THE CHLOROPLATINATE 11 



the greater part was prepared from pure iridium metal purchased 

 from Haraeus. An analysis of the chloriridate resulted as follows: — 



0-07635 grms. (NH4)2 IrCle gave 0-0330 grms. iridium. 

 Theoretical value of Ir = 0-0326 grms. 



Ammonium Bromide and Chloride: — These salts were prepared 

 by redistilling the corresponding acids and absorbing them in freshly 

 prepared ammonia water. Evaporation of the respective solutions 

 gave the desired products. 



Apparatus. 



In carrying out the solubility determinations, it was necessary 

 to agitate the solvent and solute together at a definite temperature, 

 until the solvent had become saturated with the salt in question. 

 For this purpose, tubes containing the solutions and salts were attached 

 to paddles which could be rotated in a constant temperature bath 

 of approximately forty liters. By means of a thermostat the temper- 

 ature of the bath could be controlled within 0-05°. A thermometer, 

 the readings of which had been standardized, allowed the temperature 

 to be read to hundredths of a degree. To prevent radiation a cover 

 was fitted to the top of the tank, while the sides were insulated with 

 a thick coating of felt. 



Jena test tubes of 50 c.c. capacity were used to contain the 

 solutions, while they were being agitated in the bath, except in the 

 case of the iridium solutions. Here, the amount of iridium salt 

 available was much less than for the platinum salt, while the solu- 

 bility was greater. For these reasons tubes of about 12 c.c. capacity 

 were used for the iridium solutions. The tubes were sealed with 

 rubber stoppers which had been thoroughly cleaned by boiling in 

 caustic soda solution. 



Analytical Methods. 



When equilibrium between solvent and solute had been attained, 

 the tubes were removed from the paddles and suspended in the bath 

 to allow the finely divided, yet heavy powder, to settle. When the 

 solution had become perfectly clear, a certain portion of it was drawn 

 into a weighed Sprengel pyknometer, by the aid of a glass tube, 

 bent at a right angle and having an arm long enough to reach well 

 down into the solubility tube. This arm carried a plug of cotton, 

 to retain any particles of salt that might otherwise be drawn into the 

 pyknometer. After hanging in the balance case until equilibrium 

 had been attained the pyknometer and contents were weighed. The 

 weight of salt contained in each portion of solution drawn off was 

 now determined and when this weight was subtracted from the weight 



