234« Intelligence and Miscellaneous Articles. 



that " the angle of the rhombus of the best form is that of 109° 28' 

 16" ;" precisely the result obtained by Mr. Sharpe by the use of the 

 fluctional theorem de maximis et minimis. 



MR. BUCHANS EXPERIMENTS ON THE AMALGAMATION OF SIL- 

 VER-ORES. 



Some very interesting experiments have lately been made upon 

 the process of amalgamating the ores of silver in Mexico, by Mr. 

 Buchan, at the Haciendas of Real del Monte. Considerable ob- 

 scurity has prevailed as to the mode in which the decomposition of 

 the various substances is brought about, and the silver detached 

 from its combination with sulphur, so as to be in a state to be acted 

 upon by the quicksilver. 



Descriptions of the mode of conducting the operations of amal- 

 gamating in Mexico, will be found in the works of Humboldt ; in 

 the Selections relating to Mexico, by Taylor ; and in Capt. Lyon's 

 Journal. 



The ores are mingled at first with a mixture of muriate of soda, 

 calcined copper, and iron pyrites, called magistral; the mass in a 

 short time heats, and decomposition goes on ; after which, quick- 

 silver is incorporated with it. If the heat generated be greater 

 than experience has shown to be favourable to the proper effect, 

 it is checked by the addition of lime. 



The use of the magistral has not been hitherto clearly explained : 

 from the mode in which it is prepared, it may be supposed to con- 

 sist, as Humboldt states, of the sulphates of iron and copper ; and 

 the property of heating the mass has been attributed to these salts. 



Mr. Buchan has found that the magistral contains a certain quan- 

 tity of free sulphuric acid, and that it is esteemed good very much 

 in proportion to this quantity. He has also exposed ores to amal- 

 gamation, substituting dilute acid for the magistral ; and the effect, 

 as far as the process had been conducted, was similar to that pro- 

 duced by the usual mode. 



It is possible that the oxides in the magistral, particularly that of 

 iron, may have important uses in the later stages of the operation j 

 but as the magistral, in some of the mining districts in Mexico, is 

 obtained at great expense only, it is probable that its use may be su- 

 perseded with advantage, when further experiments have been made ; 

 and, at any rate, the researches of Mr. Buchan will probably throw 

 much light on this obscure subject, which may lead to important 

 results. 



ACCOUNT OF A CHEAP AND EASILY- CONSTRUCTED BAROMETER 

 FOR MEASURING ALTITUDES, &C BY MR. J. OTLEY. 



To the Editors of the Philosophical Magazine and Annals. 

 Gentlemen, 

 Observing in a late Number of the Philosophical Magazine*, a pro- 

 posal by Mr. Nixon for determining the heights and dip of strata 

 by barometric observations, I take the liberty of offering a descrip- 

 tion of an instrument I have lately constructed, whic£, I think, par- 



* See Phil. Mag. and Annals, N. S. vol. iii. p. 11 



ticularly 



