468 



munication, read July 8, 1852, I reported the results of an exami- 

 nation of twenty-four plants or vegetable products, in twelve of 

 which fluorine was found. It will suffice to state in reference to both 

 papers, that their object is to point out, and illustrate by examples, 

 methods of readily discovering fluorine in circumstances which pre- 

 viously rendered its detection difficult. 



The more perfect of the two processes has been applied with suc- 

 cess by Professor Hoffmann to the detection of fluorine in the mine- 

 ral waters of Harrogate ; and Fresenius has introduced it into the 

 last edition of his *' Qualitative iVnalysis."* 



The researches thus referred to have been chiefly published in 

 the "Transactions" of this Society, and of the British Association, 

 but have been brought in part before the Chemical Society of Lon- 

 don. They are known in Germany, Denmark, Sweden, and Ame- 

 rica, and have been referred to by many authors in this country. 

 It is reasonable, accordingly, to infer that some knowledge of them 

 has reached Paris ; and it might have been supposed that they had 

 not altogether escaped the notice of M. Nickles, whose name ap- 

 pears on the title-page of the Journal de Pharmacie et de Chimie, 

 as editing the department of that work entitled " Une revue des 

 Travaux Chimiques publics a I'Etranger." 



I bring no charge, however, against M. Nickles. In these days 

 of multiplied monographs it would be unjust to blame any man for 

 ignorance of a single series of special researches. Nevertheless, 

 seeing that this author's name appears on the title-page of the 

 Journal de Pharmacie side by side with those of our Vice-President 

 Dr Christison, as its Edinburgh Correspondent, and of Dr Redwood, 

 the Secretary of the Cavendish Society, as its London Correspondent, 

 the countrymen of M. Nickles, may think themselves entitled to quote 

 the legal maxim, '* de non apparentibus et de non existentibus eadem 



* Fourth edition of the English translation, 1855, p. 134, stated by its edi- 

 tor, Mr J. L. Bullock, to correspond with the eighth German edition. The 

 process essentially consists in heating the silicated fluoride with oil of vitriol, 

 and condensing the gaseous fluoride of silicon in aqueous ammonia, which after 

 evaporation, re-solution in water, and desiccation, yields fluoride of ammonium. 

 Fresenius recommends the addition of " some coarse pieces of marble to insure 

 a continuous slight evolution of gas ;" but I cann't approve of this recommen- 

 dation, since the constant occurence of fluorine in shells and corals implies its 

 presence in limestiines ; and the employment of marble for the purpose indica- 

 ted risks the introduction of the very element for which we are seeking. 



