482 Intelligence and Miscellaneous Articles. 



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from the baths of Rennes, called Eaux rouges d'Alet, the author ob- 

 served, that this deposit, which he at first thought completely free from 

 arsenic, contained a small quantity of it, but could only be detected by 

 washing the gas furnished by Marsh's apparatus, bypassing it through 

 a solution of gold or silver. For this purpose the deposit previously 

 carbonized must be employed, for if the water employed to wash was 

 used instead, not the smallest quantity of arsenic was obtained ; and 

 when the deposit was used in the apparatus, so small a quantity of 

 arsenic was obtained in a given time, that no spots were procurable. 



The arsenic exists therefore in these deposits in very minute quan- 

 tity, and in the form of a compound insoluble in boiling water, even 

 when rendered strongly acid by sulphuric acid : the author ad- 

 mits, that not having obtained any arsenic by his first analysis, he 

 stated that these waters did not contain any; but he afterwards found 

 that he had been deceived by the process which he employed. 



It was demonstrated by experiments, that if in certain cases the 

 arsenic existed in the chalybeate waters in the form of a compound 

 soluble in acids, in other cases it is found in the state of an insolu- 

 ble compound ; it was also found that the insoluble arsenical com- 

 pound was so slightly attacked by nascent hydrogen in Marsh's ap- 

 paratus, that it did not contain enough to yield even very slight 

 spots, and that it was requisite to condense it in solution of gold or 

 silver to ascertain its existence. 



It remained to determine the nature of the arsenical compound 

 which acted in this manner, and the author suspected that it might 

 be sulphuret of arsenic ; the deposit had imbibed water containing 

 sulphates, and itself contained a large proportion of them, besides a 

 great quantity of organic matter ; it will then be readily imagined 

 that part of the sulphates might be converted into sulphurets under 

 the influence of the organic matter, and these acting upon the arse- 

 nical compound which previously existed in another form, might 

 convert it into sulphuret. 



Another considerable difficulty however remained ; sulphuret of 

 arsenic is considered by chemists as perfectly unacted upon by nas- 

 cent hydrogen, and if this be the case it must be admitted that the 

 ferruginous precipitates examined did not contain sulphuret of 

 arsenic. 



The author endeavoured, but in vain, to isolate the suspected sul- 

 phuret of arsenic by ammonia ; and it afterwards occurred to him to 

 determine whether the natural sulphurets of arsenic were acted upon 

 in Marsh's apparatus; for this purpose very pure orpiment and 

 realgar were reduced to fine powder, and it was ascertained that 

 the water with which they were washed contained no trace of 

 arsenic ; each of the sulphurets was then subjected to examination in 

 Marsh's apparatus, the gas liberated having been passed before add- 

 ing them, through solution of nitrate of silver for half an hour with- 

 out producing any change in it. In a quarter of an hour after adding 

 the sulphurets, the solution of silver began to be turbid ; the turbid- 

 ness at first increased very slowly, but at the expiration of six hours, 

 a considerable quantity of black precipitate was formed ; this solu- 



