1826.] Dr, Christison's Repty lo Mr. Phillip3. 25 



does not know that his fluid cannot be decolorized. He betakes 

 himself of course to your process, adds charcoal in portion after 

 portion without effect, and at last becomes satisfied that the 

 fluid will not part with its colour. But what has become of the 

 arsenic when all is over ? it is gone to be sure, — gone with the 

 charcoal. 



You say you were aware that some fluids cannot be decolo- 

 rized ; and I believe you were ; — I never said your were not. 

 But you add that you stated the fact in your paper. 1 am sorry 

 I cannot find any statement of the kind, — any hint of it even. 

 The readers of the Annals will not wonder at my imagining I 

 saw directions to boil in the author's injunctions to mix and 

 digest, — when he himself finds a statement of facts where there 

 exists not even a shadow of them. 



2. I repeat that the arsenic is sometimes removed as well as the 

 colour y when the proportion is small, even although the charcoal 

 is not boiled with the fluid. You say indeed this is not the case 

 with port-wine ; and I have said I am willing to believe you 

 correct. But try strong tea with cream and sugar. 



I mixed a solution containing one grain of arsenic with an 

 ounce of such tea ; and having ascertained pretty nearly the 

 quantity of well-washed ivory- black required for decolorizing 

 the mixture, 1 allowed it to act in the cold for two or three 

 minutes. The filtered fluid had a pale straw-yellow opalescence. 

 The silver test caused a cream-coloured precipitate ; the copper 

 test a bluish-green haze, but hardly any precipitate ; lime-water 

 a whitish haze, and very scanty precipitate ; sulphuretted hydro- 

 gen [with the previous addition of acetic acid] ; a copious 

 lemon-yellow precipitate. Hence none of the tests gave a true 

 indication, except the last; and as to that one, I find the colour 

 is brighter without the previous decolorizing process. Here then 

 is a fluid, to which your process is inapplicable, although it does 

 destroy the colour. Porter, with the same proportion of arsenic, 

 may be decolorized, so as to restore the correct action of the 

 silver test ; but lime-water and the copper test do not act at all, 

 although the colour is quite destroyed. 



3. This leads me to remark, thirdly, that your process does 

 not take away the power ivliich mam/ Jiuids possess of retaining 

 the precipitates in solution. The arsenites of lime and copper are 

 soluble in many vegetable and animal fluids, particularly when 

 they contain a free acid. But a free acid is not the only cause. 

 The porter used above, which contained an obvious quantity of 

 arsenic after decolorizatioii, did not contain a free acid ; neither 

 did the tea. This is a material objection when we consider that, 

 for satisfactory evidence on a trial, the concurrent indications of 

 many fluid tests are, in the opinion of every medical jurist, abso- 

 lutely necessary. 



To these objections I may add, that they are doubly strong 



