252 Prof. Giseke's Observations on the Tests for Arsenic. 



remarkable; but I have no doubt that Mr. Burns will now 

 regret that he has been so hasty in attributing the discordance 

 to the principles of Dr. Brinkley's solution. 



I am, sir, yours, &c. 

 Greenwich Hospital, Oct. G, 1825. E. RiDDLE. 



XXXV. Observations on the Tests for Arsenic*. By Aug. 



LUDW. GiSEKE. 



I. On the Detection of Arsenic by Lime-voater. 

 T GIVE, by way of introduction, a short account of some 

 -*■ experiments on the subject, made some time since at this 

 university, and which were occasioned by the following pass- 

 age in Berzelius's excellent Instructions in Chemistry [Lehr- 

 bnche der Chemie). Berzelius mentions in the second volume 

 of this work, p. 152 (according to Palmstedt's translation), the 

 chemical detection of poisoning by arsenic, for which he gives 

 the following process as proposed by Rose, with some addi- 

 tions of his own : " Cut up the coats of the stomach, and place 

 them in the liquid, which is boiled with a few drachms of 

 caustic potash, in order to dissolve anyarsenious acid that might 

 be contained in it. The solution obtained is filtered, heated 

 till it boils, and during the boiling mixed with nitric acid, 

 which is added in small portions as long as any thing sepa- 

 rates, and till the liquid has become strongly acid, clear, and 

 of a bright yellow colour. It is filtered while hot, afterwards 

 nearly, not completely, saturated with carbonate of potash, and 

 made to boil, in order to expel the cai'bonic acid ; then it is 

 boiled with clear lime-water as long as a precipitate is formed. 

 The lime-water first saturates the excess of acid, and then 

 precipitates with the arsenious acid as arsenite of lime, and with 

 the phosphoric acid and other animal substances decomposed 

 in the nitric acid. If instead of saturating the acid with lime- 

 water, you add first caustic alkali, till the liquid becomes al- 

 kaline, and then add lime-water, no precipitate will be formed, 

 because the arsenite of lime is held in solution by the al- 

 kali." 



It has been already observed by Hahnemann, that the ar- 

 senite of lime is dissolved even by the weakest acid of any kind ; 

 but no one noticed before Berzelius that it was also soluble in a 

 saturated alkaline solution ; and it also contradicted the expe- 

 riments made by Prof. Schweigger in his chemical lectures, 



* From Schweigger's Juunial, B;uid xiii. p. .359. — This article is con- 

 densed from several lectures given by the author at the Physical Seminary at 

 Halle. 



which 



1 



