[ 46 J 



XI. On the Formula: representing Chahasie^ in a Letter to 

 Professor Johnston. % R. Phillips, F.R.SS., L. S,- E. 



My dear Johnston, 

 nnO your paper, contained in the last Number of this Journal, 

 ■*- " On some apparent exceptions to the law, that like cry- 

 stalline forms indicate like chemical formulas," you have ap- 

 pended this note : " If Mr. Phillips will look at the formula 

 for chabasie given in the table, his difficulty about the mu- 

 tual replacement of potash and soda -iVill or ought to dis- 

 appear." 



Before however doubts can cease to exist, clear grounds 

 must be stated for their removal ; allow me therefore to direct 

 your attention to the very different statements which you 

 have made at various and not very distant periods, respecting 

 the composition of chabasie. 



In the London and Edinburgh Philosophical Magazine, 

 vol. ix. p. 168, you observe that "chemists have recognised 

 two varieties of chabasie ; one from Aussig in Bohemia, and 

 from Fassa, analysed by Hoffman, and from Faroe analysed 

 by Arfvredson; represented by the formula, 



N yS^+ 3 AS'+ 6Aq, 



and another from Nova Scotia, analyseil by Hoffman, from 

 Gustafsberg, by Berzelius, and from Kilmacolm, by Mr. 

 Connell, represented by the formula, 



N ls^+ 3AS^ + GAq." 



As chemical formulae the above have no meaning; the latter, 

 I presume, was intended to include the mincralogical formula 

 of lime chabasie, as given by Berzelius, No?weau Sijstemc de Mi- 

 neralogic (p. 219), CS^ + 3 AS- + 6 Aq. But you have omitted 

 to adopt a necessary precaution in employing mincralogical 

 lormuhB ; for Berzelius says, " pour cviter toute espcce de 

 confusion, qui pourrait provenir des deux sortes de formules, 

 je marquerai les mineralogicjues en caractcres italiques." 



In the Report of the British Association, vol. vi. p. 176, 

 you have thus represented 



Na-n 



« Chabasie K« I Si^ + SAlSi- + ISH." 



In the above formula, owing, as I suppose, to the slipping 

 of one of the marks representing an equivalent of oxygen, 



