S22 On the detection of Arsenic. 



successively in the form of sulphuret, metal, and oxide ; and 

 he discards the fluid tests for liquid mixtures entirely, except 

 as trial tests. Both he himself and Dr Turner have satisfied 

 themselves, that the physical characters of the metal and oxide, 

 when successively formed in a small tube by reduction and sub- 

 sequent oxidation, may be determined accurately with a hu7i- 

 dredth part of a grain. This is a degree of delicacy which, 

 considering that decisive evidence is required, is not equalled 

 even by the hquid tests. 



In the Annals of Philosophy for last July, Dr Christison has 

 replied to some comments which Mr Phillips had made not 

 long before on his paper. As Mr Phillips' criticisms referred 

 only to a defence of his process for decolorizing coloured ar- 

 senical fluids by animal charcoal, and Dr Christison states, in 

 his reply, that he considers the necessity of that process to be 

 completely superseded by the equal, if not superior delicacy, 

 and universal applicability, of his own, it is unnecessary to say 

 any thing farther of the dispute, than that Mr Phillips'' process 

 certainly appears Uable to material fallacies, although Dr Chris- 

 tison, from misunderstanding his directions, had somewhat ex- 

 aggerated one of them. 



The Journal de Pharmacie for last April likewise contains 

 some comments on Dr Christison's paper by M. Dublanc of 

 Paris. It is evident that the writer has wholly misunderstood 

 the character of the paper he criticises, and is utterly ignorant 

 both of the grounds on which Dr Christison objects to the pro- 

 cesses of Rose, Rapp and Orfila, and of the circumstances on 

 which is founded the proof of the delicacy and universal appli- 

 cability of his own. Nor indeed is this to be wondered at, as 

 M. Dublanc has consulted, not the original paper, but some 

 garbled extract in a German Journal. 



6. On Cqfeine. 

 In 1821, M. Robiquet of Paris published an elaborate analy- 

 sis of the coffee-bean, in which he announced the existence of a 

 new vegetable principle of a crystalline nature. This principle, 

 which was denominated Cqfeine, has been since examined by M. 

 Pelletier, and M. Garot. Both of these experimenters have con- 

 firmed completely the researches of Robiquet, regarding the cha- 



