296 Dr. Turner on the Ores of Manganese. 



The principal sources of error in this method are the two 

 following : loss of chlorine, by smelling repeatedly, and expo- 

 sure to the air when the gas is absorbed by pure water ; and 

 oxidation by the air when the absorption is made directly by 

 means of the solution of iron. The small flask and inverted 

 tube are apt to retain the odour of chorine, and should there- 

 fore be rinsed out with the absorbing liquid. It should be 

 remembered, also, that a given quantity of chlorine will emit a 

 more or less distinct odour, according as it is less or more 

 diluted. But by operating always in the same manner, and 

 employing such weights of different ores, that equal quantities 

 of the solution may contain nearly equal quantities of chlorine, 

 it is easy to be independent of these errors of manipulation, by 

 causing them to affect each experiment to the same degree. 

 It will accordingly be found, with a little practice, that results 

 of surprising uniformity may be thus obtained ; and even the 

 constitution of pure oxides of manganese may be ascertained 

 by this method, almost with the same accuracy as by directly 

 determining the quantity of oxygen. 



PHENOMENA OBSERVED AT THE LAST ERUPTION OF 

 MOUNT VESUVIUS IN 1828. 



BY DR. E, DONATI. 



A FTER the tremendous eruption of 1822, Vesuvius re- 

 "^^ mained silent and apparently calm, until the 14th of 

 March, 1828. At this time the volcano presented to the 

 eye of the curious a truncated cone, steep and difficult of 

 ascent, two hundred toises * in height : and a vast crater, 

 half a mile in diameter, but of which the periphery, owing to 

 the many irregularities of its outline, was nearly three miles in 

 extent. The depth of the interior, which resembled an in- 



* The celebrated Humboldt, on the 25th of November, 1822, took the baro- 

 metrical measurement of the greatest cone, and found that the point Del Palo, 

 was at an elevation of 223 . 6 toises above the plane of the cone, where travellers 

 usually leave their horses to proceed on foot. This height is now diminished by 

 fifteen toises j the materials which formed the summit having fallen into the 

 interior of the crater. 



