Dr. Fresenius on the Detection of Arsenic. 255 



action, where the oxygen is capable of forming a chemical 

 compound of a higher degree of oxygenation, and like other 

 secondary actions of a similar nature, is variable in its amount. 



8. The disenjiagement of the cation and anion of an elec- 

 trolyte in equivalent proportions is not always effected, as is 

 commonly represented, by their simultaneous transfer in op- 

 posite directions to their respective electrodes, in the exact 

 proportion of half an equivalent of each ; but is sometimes 

 brought about by the transfer of a whole equivalent of the 

 anion to the zincode, whereby a whole equivalent of the cation 

 is left uncombined at the platinode ; or by transfer of unequi- 

 valent portions of each in opposite directions, making however 

 together a whole equivalent of matter transferred to one elec- 

 trode or the other; or speaking more correctly, by the transfer 

 of a quantity of matter capable of exerting one equivalent of 

 chemical force, so that when the anion transferred to the zin- 

 code exceeds half an equivalent, the cation transferred to the 

 platinode is in an equal proportion less than half an equiva- 

 lent, and vice versa ; the anion and cation set free being always 

 in equivalent proportions. We have, however, in no case 

 observed the transfer of a whole equivalent of the cation to 

 the exclusion of the anion. 



These facts are, we believe, irreconcilable with any of the 

 molecular hypotheses which have hitherto been imagined to 

 account for the phaenomena of electrolysis, nor have we any- 

 thing more satisfactory at present to substitute for them ; we 

 shall therefore prefer leaving them to the elucidation of fur- 

 ther investigation, to adding one more to the already too nu- 

 merous list of hasty generalizations. 



XL I. On an improved Method for the Detection and Qiiati" 

 titative Determination of Arsenic. By Kemigius Frese- 

 nius, M.D.* 

 T^HE greater part of this paper is occupied with the dis- 

 -*- cussion of the medico-legal questions arising in cases of 

 poisoning; the author advocates the interference of the legis- 

 lature to render it imperative on chemists to pursue a given 

 method in seeking for the presence of poisons : and after 

 pointing out the sources of uncertainty in all the methods em- 

 ployed hitherto for the detection of arsenic, he proposes a new 

 one, which he alleges is free from every objection, which me- 

 thod is the result of many investigations pursued by himself 

 in conjunction with Dr. von Babo. 



* Communicated by the Chemical Society; having been read April 15, 

 1844. 



