Mr. Brooke on some undescribed Minerals. 277 



Kupferschaum. 



I do not find any analysis published of the mineral termed 

 Kvpfcrschaum by the Germans, which is the same as the fibrous or 

 flaky bright green substance found at Matlock. 



It dissolves entirely and with effervescence in muriatic acid. 

 From this solution a bulky precipitate is thrown down by caustic 

 potash, a considerable part of which is redissolved by an excess 

 of the alkali, leaving a residuum of hydrate of copper. If the solu- 

 tion be filtered to separate the copper, and acetous acid be added, 

 a white flocculent precipitate appears, which may be redissolved by 

 an excess of acid or of alkali. As this is a marked character of 

 oxide of zinc, I conclude that the mineral is a carbonate of copper 

 and zinc. 



Art. XII. On a Mountain Barometer constructed with an 

 Iron Cistern. By J. Newman, Philosophical Instrument- 

 Maker to the Royal Institution of G/reat Britain. 



[To the Editor of the Quarterly Journal.] 

 Sir, 



I take the liberty of sending you an account of an alteration I 

 have made in the construction of Mountain Barometers, and which 

 has been declared highly satisfactory and important, by those who 

 have made trial of instruments so constructed. The object has 

 been to correct those defects and errors which arise from the use 

 of a wooden cistern and leather bag, in the common instrument. It 

 has been found that when the cistern is made of a wood sufficiently 

 sound and close-grained to permit of the pressure required from 

 the screw to make the instrument portable, that it is so impervious 

 to air, as not to allow it to pass with sufficient freedom, and con- 

 sequently, that when the instrument is used at any great altitude, 

 the mercury cannot fall into the cistern except with considerable 

 difficulty, and a long time is required before an accurate observa- 

 tion of the air's pressure can be made ; most generally, however, the 

 cistern is sufficiently pervious to air, but it is then found that on 



