M. Kessler on the Equivalent of Antimony. 307 



Kekule has found that maleic acid, when acted upon by the 

 same reagents, yields the same bodies. 



In conclusion, he developes his views as to the relations between 

 fumaric acid and its allied substances. He establishes a close 

 and interesting analogy between fumaric acid and ethylene. 

 Fumaric acid stands in the same relation to malic acid as 

 ethylene does to alcohol; it stands to dibromosuccinic acid as 

 ethylene does to bromide of ethylene ; and to monobromosuccinic 

 acid as ethylene to bromide of ethyle, and so on. Tartaric acid 

 is to fumaric acid what glycol is to ethylene. In fact tartaric 

 acid is obtained when the bromide of fumaric acid, that is, dibro- 

 mosuccinic acid, is heated with oxide of silver, just as an ether 

 of glycol is obtained when a silver salt acts upon bromide of 

 ethylene. 



In PoggendorfPs Annalen for 1855, Kessler described a volu- 

 metric method of estimating arsenic and antimony, by which 

 he made a determination of their atomic weights. The method 

 consisted in oxidizing these substances, which were employed in 

 the form of arsenious and antimonious acids, to arsenic and anti- 

 monic acids by means of a standard solution of bichromate of 

 potash ; the excess of bichromate of potash was determined by 

 means of a standard solution of protochloride of iron. The 

 applicability of this method depends upon the fact that proto- 

 chloride of iron reduces bichromate of potash, but does not 

 affect arsenic or antimonic acid. Kessler has since then made * 

 some additional experiments, partly confirming and partly recti- 

 fying previous results. 



From these experiments he concludes that the atomic weight 

 of arsenic is 75*15. 



For the atomic weight of antimony, Kessler's previous experi- 

 ments led to the number 12378. In his recent experiments, 

 in which some sources of error, to which his previous methods 

 were liable, have been avoided, he has obtained different results. 



Pure oxide of antimony was prepared, and was further puri- 

 fied by sublimation in a porcelain tube in a current of carbonic 

 acid ; a given weight of this was partially oxidized by a given 

 weight of pure chlorate of potash, and the oxidation completed 

 by means of a standard solution of bichromate of potash ; the 

 excess of the latter was estimated by a standard solution of 

 protochloride of iron. In this way six experiments gave num- 

 bers for the equivalent of antimony, varying between 121*67 and 

 122-58, the mean being 122*16. 



In another case, in which pure metallic antimony was oxi- 



* PoggendorfF s Annalen, vol. cxiii. p. 134. 



