344 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 54 



81.66 81.71 



81.55 81.63 



81.81 81.56 



81.86 81.58 



81.54 81.67 



81.68 81.84 



Mean, 81.702, ± .014 



Hence Cr = 53.56. 



Next in order we have to consider two papers by Kessler, who em- 

 ployed a peculiar volumetric method entirely his own. In brief, he com- 

 pared the oxidizing power of potassium dichromate with that of the 

 chlorate, and from his observations deduced the ratio between the mo- 

 lecidar weights of the two salts. 



In his earlier paper ' the mode of procedure was about as follows : 

 The two salts, weighed out in quantities having approximate chemical 

 equivalency, were placed in two small flasks, and to each was added 

 100 cc. of a ferrous chloride solution and 30 cc. hydrochloric acid. The 

 ferrous chloride was added in trifling excess, and. when action ceased, 

 the amount unoxidized was determined by titration with a standard solu- 

 tion of dichromate. As in each case the quantity of ferrous chloride was 

 the same, it became easy to deduce from the data thus obtained the ratio 

 in question. I have reduced all of his somewhat complicated figures to 

 a simple common standard, and give below the amount of chromate 

 equivalent to 100 of chlorate: 



120.118 

 120.371 

 120.138 

 120.096 

 120.241 

 120.181 



Mean, 120.191, ± .028 



Hence Cr = 52.20. 



In his later paper ^ Kessler substituted arsenic trioxide for the iron 

 solution. In one series of experiments tlie quantity of dichromate needed 

 to oxidize 100 parts of the arsenic trioxide was determined, and in an- 

 other the latter substance was similarly compared with the chlorate. 



1 Poggend. Annalen, 95, 208. 1855. 

 2Poggend. Annalen, 113, 137. 1861. 



