1 882.] Mineralogy 163 



caoutchouc, the tin foil being connected to a galvanometer. By 

 now compressing the crystal in a vise or otherwise, electricity is 

 developed and may be measured by the galvanometer. The 

 electricity developed is the opposite of that produced by heating 

 a crystal, — that is to say, the extremity of the crystal which be- 

 comes positive on heating, becomes negative on compression. 

 On releasing the pressure, electricity of an opposite kind is pro- 

 duced. The authors find that the production of electricity by 

 pressure can only be obtained with hemihedral crystals having 

 inclined faces. By combining a number of such crystals in a pile, 

 they have invented a new apparatus for producing electricity. The 

 amount of electricity developed varies for different minerals. 

 They find, for example, that a section of quartz, cut perpendicular 

 to the main axis, evolves more electricity than a similar section of 



Note on Gold. — There is a simple method for the detection of 

 gold in quartz, pyrite, etc., which is not generally described in 

 the mineralogical text-books. It is an adaptation of the well- 

 known amalgamation process, and serves to detect very minute 

 traces of gold. 



Place the finely powdered and roasted mineral in a rest tube, 

 add water and a single drop of mercury ; close the test tube with 

 the thumb and shake thoroughly and for some time. Decant the 

 water, add more and decant repeatedly, thus washing the drop of 

 mercury until it is perfectly clean. The drop of mercury contains 

 any gold that may have been present. It is therefore placed in a 

 small porcelain capsule and heated until the mercury is volatilized 

 and the residue of gold is left in the bottom of the capsule. This 

 residue may be tested either by dissolving in aqua regia and ob- 

 taining the purple of Cassius with protochloride of tin, or by taking 

 up with a fragment of moist filter paper, and then fusing to a 

 globule on charcoal in the blowpipe flame. 



It is being shown that gold is much more universally distributed 

 than was formerly supposed. It has recently been found in Ful- 

 ton and Saratoga' counties. New York, where it occurs in pyrite. 

 It has also been discovered in the gravel of Chester creek, at 

 Lenni, Delaware county, Penna. In one of the Virginia gold 

 mines wonderful richness is reported. $ 160,000 worth of pure 

 gold having been taken from a space of three square feet 



A New Textbook of Mineralogy.— The mineralogists of 



.. " -"^ ":':-■ "■' ":; :"^ ^ ' 



tion of the physical, optical 'and crvstallographie characters ot 

 minerals, and of the various delicate mean^ of investigation at 

 the command of modern mineralogists. Under the head of 

 Physical mineralogy an account is given of the latest discoveries 



