178 



S. E. Moody — Hydrolysis of Salts. 



The sulphuric acid set free by hydrolysis upon boiling with 

 the iodide mixture was then found by the iodide-iodate reac- 

 tion, one gram of potassium iodide being in each case dissolved 

 in 10 cm3 of a solution of potassium iodate (30 grms. to a liter) 

 and added to the measure of chrome alum in the Yoit flask. 

 The mixture was boiled thirty minutes with a current of 

 hydrogen to aid in removing the iodine liberated to the Drexel 

 flask containing about 3 grams of potassium iodide dissolved 

 in water. The iodine collected in the receiver was estimated 

 with sodium thiosulphate as in previous experiments. That 

 the hydrolysis of the sulphate had been complete was shown 

 by dissolving the washed precipitate in nitric acid and testing 



the sol 

 found. 



ution wit 



h barium 



chloride, no b£ 



irium sulpha 



te being 









Table IV. 









Approx. 



N/10 

 chrome 



alum. 



Time in 

 minutes. 



Na 2 S 2 3 . 



I. 



Cr 2 3 



corresponding to 



S0 3 , equivalent of 



iodine set free. 



Excess 



of 

 Cr 2 3 

 (Basic.) 



cm 3 . 





cm 3 . 



grm. 





grm. 



grm. 



25 



30 



23-50 



0-29J5 





0-0583 



0-0059 



25 



30 



23*45 



0-2908 





0-0582 



0-0060 



25 



30 



23-40 



0-2902 





0-0580 



0-0062 



25 



30 



23-45 



0-2008 





0-0582 



0-0060 



25 



30 



23-44 



0-2907 





0-0581 



0-0061 



The fact that more chromic oxide is contained in the alum 

 than corresponds to the S0 3 found by the iodide-iodate reac- 

 tion in the complete hydrolysis of the salt shows at once that 

 this particular preparation of chrome alum, like many ordi- 

 nary commercial alums, is basic. 



Tin. 



In experimenting with salts of tin the difficulty is to obtain 

 a salt of definite composition with which to start. The double 

 salt of stannic chloride and potassium chloride was selected as a 

 suitable salt for determining the character of the hydrolysis of 

 stannic chloride. This salt was prepared by adding stannic 

 chloride to a cold saturated solution of potassium chloride. 

 The material was then filtered, washed and dried in a vacuum 

 desiccator. 



The tin content of this salt was found by precipitating 

 stannic acid with the iodide-iodate mixture, igniting and 

 weighing the stannic oxide thus obtained. Results of these ex- 

 periments follow in Table Y. 





