OF ARTS AND SCIENCES. 13 



lodo-sulphnte of RoseocohaJt. — When a solution of potassic iodide 

 is added to one of the soluble sulphate of roseocobalt a beautiful cin- 

 nabar-red crystalline salt is thrown down, which may be dissolved 

 without much difficulty in hot water, and crystallizes from the solution 

 in granular crystals of an intense orange-red color. This salt has 

 essentially the formula Co2(NH3),o(SOJJ2+20H2, which is that of 

 the iodo-sulphate described by Krok, and obtained by the action of 

 iodine upon a boiling solution of ammonia and cobaltic sulphate. 

 Krok's analyses agree fairly well with the requirements of tlie formula. 

 I found, however, that the salt precipitated as above varied in different 

 preparations not inconsiderably. I prepared the salt also from the 

 ordinary sulphate of roseocobalt for the sake of comparison, but could 

 detect no really essential difference between the two. The following 

 are the results of my analyses : — 



Of the iodo-sulphate from the ordinary red sulphate of roseocobalt : — 



I. 0-6300 gr. gave 0-2673 gr. SO.Co = lG-15% cobalt. 

 0-4284 gr. gave 0-1170 gr. silver = 32-12% iodine. 

 0-5689 gr. gave 0-351 G gr. SO,Ba= 25-4G^ So,. 



Of the iodo-sulphate from the soluble sulphate : — 



II. 0-4045 gr. gave 0-1776 gr. SO,Co = 16-72% cobalt. 

 0-4045 gr. gave 0-17G3 gr. SO,Co= 16-60% cobalt. 

 0-4G47 gr. gave 0-1096 gr. silver = 27-76% iodine. 

 0-4935 gr. gave 0-3027 gr. SO,Ba = 25-27% SO,. 

 TIL 0-3579 gr. gave 0-1442 gr. SO,Co = 15-33% cobalt. 

 0-7586 gr. gave 0-3816 gr. silver = 27-18% iodine. 

 0-7099 gr. gave 0-4308 gr. So.Ba = 25-32% SO,. 



The formula Co,(NH3)io(SO,) J,+20Il2 requires : — 



Calculated. i. ii. m. 



Cobalt, 15-33 16-15 16-66 (mean) 15-33 



Iodine, 32-99 32-12 27-76 27-18 



SO,, 24-93 25-46 25-27 25-32 



These analyses show at least that the reaction between potassic iodide 

 and the soluble sulphate is less definite than in the case of the iodide 

 and the ordinary sulphate. Krok states that he did not obtain sul- 

 phate of xanthocobalt by the action of argentic nitrite upon iodo- 

 sulphate of roseocobalt, but only a rose-red solution, giving off nitrons 

 acid with the stronger acids. I found, however, that the iodo-sul[)hate 

 obtained from the soluble sulphate of roseocobalt, when digested with 



