3^6 Anahjis of S/tel. — Espenmtiils on Galvmii/iit. 



called determinative, becaufe it is not ufcd until it has ptevioully been afcerta\ncd that the 

 iron contains manganefe, and that nothing remains but to find its quantity. It is per- 

 formed by diflblving in the nitric acid a known weight of iron or of fteel, containing man- 

 ganefe, and, after having evaporated the folution, by Rrongly calcining the ferruginous re- 

 fiduc, which is treated with more diluted nitric acid, into which a certain quantity of fugar 

 has been put. By this means (fays Bergman) the manganefe will be diffolved, and the 

 oxide of iron will remain untouched. 



Thefc procefTes, carefully repeated, did not afford me the fame refults. I mud even fay 

 that they are falfe, and capable of leading to erroneous conclufions. In faft, with legard 

 to the firft, it is known that nitrate of pot-afli, dccompofed in a crucible of pure earth or fine 

 fdver, leaves the pot-afli in the form of a mafs of a greenidi or blueidi colour. It is in vain 

 to obje£\, that this colour is owing to the manganefe contained in the pot-afli of commerce ; 

 for this alkali, when purified by alcohol, prefents the fame phenomena. And even fuppofing 

 it to be a certain fign of the prefence of manganefe, it would alfo prove a fource of error, 

 becaufe the nitrate of pot-afh, and pot-afli alone, exhibit this colour by fufion. 



Pure iron itfelf might produce deception in this refpecli for, when it has been oxided by 

 the nitrate of pot-afli, it combines by the afliftance of the alkali with tlie filiceous matter of 

 the crucible, and forms a glafs which has often a greenifli colour. Common crucibles alfo 

 are not without inconvenience ; for they may contain the oxide of manganefe, which is well 

 known to be often mixed with eanhy matters. 



The fecond method of Bergman is attended with ftill more danger of error than the 

 firft, by fixing the opinion of the exiftence of manganefe, and producing a decifion with 

 regard to its hippofed quantity. 



Bergman, who was perfuaded that the nitric acid mixed with fugar does not diffolve (the 

 oxide of) iron, muft frequently have attributed appearances to manganefe which really arofe 

 from iron only ; for we have proved, that the vegetable acid which is formed in this 

 operation dirtblvcs a confiderable quantity. 



III. 



Extras of a Letter from Mr. HuMBOLDTto Mr. BlVMENBACH, containing new Experiments 

 on the Irritation caiifed by the Metals with RefpeSl to their different ImpreJJions on the Organs 

 of Animals *. 



M, 



.R. Humboldt is one of the phllofophers who has made the mort; numerous obfervi- 

 tions on the phenomenon difcovered by Galvani concerning the irritability produced by the 

 contadl of different metals with the parts of animals in which the principle of life is appa- 

 rently extinguiflied. As long ago as the year 1795 he obfervcd that the animal irritability 

 was augmented by the oxygenated muriatic acid. Not having difcontinued his attention 

 to this objeft, the perufal of the phyfiological writings of Reii, and his correfpondence with 

 Scarpa and Volta, afforded him indications for new enquiries, of which he has occafionally 

 had the courage to make himfelf the fubje£l. 



• This Letter forms part of Gren's (German) Journal of Natural Phllorophy for the month of Oftobcr laft. 

 The cxiraft was read 10 the lofliiule of France, by Citizen Gufion. 



•'In 



