1826.] Dn Christison's Reply to Mr. Phillips. 23 



of vapour, until the metallic coil becomes incandescent, inflam- 

 ing ether, sulphur, essential oils, streams of hydrogen and car- 

 buretted hydrogen gases, camphor, and gunpowder. 



These processes continue until the pure fluid is consumed by 

 spontaneous evaporation, the impurities remaining. 



In mixtures of oxygen and hydrogen, the gases are ready for 

 combination, and the wire acquires a most intense heat, fre- 

 quently detonating them while in the fluids and solids ; their 

 vapour is required to be decomposed by the heat of the coil, 

 before the gases are present to favour the combination. This 

 proves the accuracy of the above theory. 



Article VI. 

 Reply to Mr, Phillips. By R. Christison, MD. 



SIR, Edinlurgh College, jipril 25, 1826. 



I AM sorry I have been so long in acknowledging your invi- 

 tation conveyed in the Annals of' Philosophy for last October; 

 namely, that I would repeat your experiments on decolorizing 

 arsenical fluids with animal charcoal, and candidly state the 

 results. The delay has arisen chiefly from my wish, that you 

 might see, at the same time with this answer, some further 

 remarks I have published on the detection of arsenic, in the 

 second volume of the Edinburgh Medico-Chirurgical Transac- 

 tions. 



The two first criticisms you have done me the honour of mak- 

 ing on my objections have nothing whatever to do with your 

 decolorizing process ; and are intended, you say, as a criterion 

 for trying the trustworthiness of my experiments. 



If I ever have occasion to make public use of my paper on 

 arsenic again, I shall be happy to avail myself of the correction 

 Contained in your first criticism. I must have had my head full 

 at the time of Orfila and Smith, two of my standard authors ; 

 and thinking naturally of the books generally read by students 

 of medical jurisprudence, rather than of all those actually in 

 existence, I unfortunately wrote most , instead o^ some authors. 



Do not be so unmerciful, however, as to conceive me ignorant, 

 that oxide ofarsenicisthe better of [for] a little charcoal to reduce 

 it. I find, indeed, that in the note which gave origin to this 

 accusation, there is an ambiguity which might lead one, who 

 had never read a chemical book before, to omit the charcoal. 

 But you must have seen that when I said " the charcoal of the 

 black flux is not necessary in the process," I meant the process 

 in the textj — the process for reducing the sulphuret ; and I 

 distinctly remember that my reason for introducing the clause 



