Prof. Giseke's Observations on the Tests/or 'Arsenic. 253 



which showed that arsenite of lime could not be dissolved 

 even by a great excess of alkali. In these experiments, to li- 

 quids poisoned with arsenic, caustic potash as well as soda and 

 ammonia were purposely added ; and innnediately on adding 

 lime-water, a very copious precipitate of arsenite of lime was 

 produced. 



Prof. S. considered this subject the more worthy of being 

 investigated, as it surprised him that so distinguished a che- 

 mist as Berzelius, — who is so justly respected as the first ana- 

 lyst of our age, — should be opposed to nature in so simple a 

 process. Besides, the rule laid down by this careful naturalist 

 had been already pretty generally admitted. Thus Geiger, in 

 his new and valuable Handhuche der Pharmacie, p. 431, says 

 " that the precipitate produced by lime-water in a pure aqueous 

 solution of arsenious acid might be dissolved hy free acids or 

 alkalis." And Buchner, in his ToxiJcologic, p. 405 : " Lime- 

 water will produce a white precipitate as well in arsenious as 

 in arsenic acid. In order to produce this effect, neidier any 

 free acid nor free lime-water must be in it." In x-eality there 

 may be a great excess of lime-water, without the result being- 

 disturbed by it ; on the contrary, it is beneficial to apply lime- 

 water abundantly : on which account Fischer justly recom- 

 mends rather to put the solution of arsenic into lime-water, 

 than the reverse, because the lime-arsenic is dissolved even by 

 an excess of arsenious acid. But since neither arsenite nor 

 arseniateof lime are dissolved, with any predominance of potash, 

 soda, or ammonia ; how was it that Berzelius obtained no 

 precipitate with alkali in excess ? The followmg experiment 

 made by Prof. Schweigger in his lectures on chemistry will 

 explain it. 



Prepare an arsenical liquid, pour it into three glasses, and 

 add to one portion an excess of caustic potash; to the second, 

 excess of caustic soda; and to the diird, excess of caustic am- 

 monia. On adding lime-water, a deposit of arsenite of lime 

 %vill be equally formed in each of the glasses. Now add to 

 each a few drops of acid, (for instance, nitric acid,) yet so that 

 in all the alkali shall predominate. Whilst no solution of die 

 precipitate will take place in the glasses diat have the potash 

 and soda in them, it will immediately begin in that with the 

 ammonia: and all the arsenite of lime will be finally dissolved, 

 although die ammonia be not saturated by the acid which has 

 been added. Of course the solution will take place in the 

 three glasses when any acid is in excess ; yet on saturating 

 the acid with alkali, the precipitate will be* re-formed imme- 

 diately in those glasses that contain the potash or soda, but 



not 



