Mr. G. Bird's Observations on indirect Chemical Analysis. 229 



substance, will not be attacked either by nitric acid of any de- 

 gree of dilution, nor by a solution of blue vitriol. The vol- 

 taic association of one substance with the other is easily ef- 

 fected by connecting one end of an iron wire with the positive 

 electrode of a pile, and by plunging for a few minutes the 

 other end of the wire into a solution of nitrate of silver. 



I am just about to write a paper on this interesting sub- 

 ject. I am, my dear Sir, yours very truly. 



Bale, Dec. 31, 1837. C. F. Schcenbein. 



XXXIII. Observations on indirect Chemical Analysis, By 

 GoLDiNG Bird, F.L.S. F.G.S., Lecturer on Experimental 

 Philosophy at Guy's Hospital, Sfc.^ 



/^ASES constantly fall under the notice of the analytic 

 ^^ chemist, in which, from the difficulty of separating one 

 substance from another without a tedious operation, or from 

 the absolute impossibility of effecting this separation in any 

 thing like a perfect manner, the process of indirect analysis, 

 as it has been termed, is particularly applicable. Thus, if 

 whilst engaged in the analysis of the ash of an organic sub- 

 stance in which both potash and soda are contained, we re- 

 quire the quantitative amount of each base, almost every pro- 

 posed process will to a certain extent fail. It is true that by 

 the aid of hydro-fiuosilicic acid, or the double chloride of 

 platinum and sodium, we may obtain approximations to the 

 truth, but even then the results obtained by these necessarily 

 tedious processes are by no means so exact as those obtained 

 by the aid of indirect analysis. A formula for the resolution 

 of the last-mentioned problem (the quantitative estimation of 

 potash and soda in mixtures of these bases) was proposed in 

 Berzelius's work, Sur V Analyse des Corps inorganiques, 1827, 

 by the French translator; but this was certainly very tedious 

 and not sufficiently comprehensive in its details. Poggendorff, 

 in the third number of the invaluable " Handwbrterbuch der 

 reinen und angewandten Chemie von Liebig u. Poggendorif," 

 has given two formulae for the same purpose, which have the 

 advantage of possessing considerable simplicity and of being 

 applicable to the resolution of several analogous chemical 

 problems. For the assistance of those who may not have an 

 opportunity of consulting the original work, I have made the 

 following abstract of the mod6 proposed by Poggendorff. 



If the substances are bases which form with acids neutral 

 salts of known composition, we take an exactly weighed 



• Communicated by the Author. 



