116 Dr.Apjohn on a new Compound of Iodide of Potassiumf 



filter being well washed, the solution was evaporated to dry- 

 ness in a carefully counterpoised capsule, and then accurately 

 weighed. The following are the results of three experiments 

 thus conducted. 



IK IK 



(per cent.) 



3*37 grains gave 0*43 12'75 



8-00 1-03 12-87 



9-40 1-13 12-02 



The mean therefore of the numbers in the third column, 

 or 12*55* is the quantity of iodide of potassium as obtained 

 by me in 100 grains of the compound. 



The next step was to investigate the iodine associated not 

 with the potassium but with the oil, and to effect this the fol- 

 lowing was the course first pursued. 



A known weight of the compound was decomposed by a 

 slight excess of an alcoholic solution of potash, and the whole 

 was evaporated to dryness, by which the oil was partly vola- 

 tilized and partly decomposed. Heat was now cautiously ap- 

 plied, so as to reduce the iodate, which I have already stated 

 to be always formed in such experiment, to the state of iodide 

 of potassium, but not to volatilize any of the latter salt. The 

 residue, first permitted to cool, was treated with distilled 

 water, and passed through a filter to separate the carbon. 

 The filter was well washed, and the solution, having been re- 

 duced to a small bulk by evaporation, was precipitated by 

 nitrate of silver, and the iodide of silver, first edulcorated 

 three or four times with cold distilled water containing a few 

 drops of ammonia, was finally dried, melted and weighed. 



In an experiment in which 10*33 grains of the compound 

 were employed, the iodide of silver amounted to 7"-l'l grains, 

 equivalent to 3'95 of iodine, or 38*24 for 100 grains of the 

 compound. Now, if from this we subtract 9*58, the iodine in 

 the 12*55 grains of iodide of potassium which we have already 

 found to exist in 100 of the compound, we shall get for the 

 per centage of iodine in union with the oil the number 28*66. 



Fearing that the heat applied in reducing the iodate of 

 potash to iodide of potassium, might have either been insuffi- 

 cient for the purpose or have volatilized some of the latter 

 salt, I recommenced the estimation of the amount of free 

 iodine, or rather of that united to the oil, by a somewhat dif- 

 ferent process. 



A known weight of the substance was introduced into a 

 test tube with water and zinc filings, and the other end being 



• This contains 9*58 grains of iodine. 



