114 THE AMERICAN MONTHLY [Apr 



American Postal Microscopical Club. 



NOTES ON SOME OF THE SLIDES. 



Artificial Onyx. — It is not commonl}^ known that nearh^ 

 all of the onyx used in the artsiscolored by artificial means ; 

 the orig-inal color of the ag-ate being- usually a white, or va- 

 rying- shades of g-ray and white, the bands of color repre- 

 senting varying degrees of density, or,more properly, per- 

 meability ; which bands are supposed to be produced by 

 different deg-rees of rapidity with which the formation 

 takes place, thoug-h doubtless many other causes, such as 

 temperature, pressure, etc., contribute to produce the re- 

 sult. Advantag-e is taken of this structure to effect the 

 coloring- which is done in the case of black onyx by immer- 

 sing- the stone in a mixture of h/'^ey and water, where it 

 remains several weeks at a high temperature. It is then 

 boiled in sulphuric acid, which carbonates the sacharinous 

 matter which has penetrated the stone, thus rendering cer- 

 tain bands an intense black, while others, remaining- unaf- 

 fected, appear by contrast, of a pure white. Various col- 

 orations may be produced by different chemical reactions. 

 What is the difference in the molecular .structure of the 

 two bands of equal thickness, one of which is penetrated 

 by the honey solution to the depth of an inch or more, while 

 the other, of the same atomic elements, and apparently of 

 the same hardness,remains absolutely unaffected ? Agates 

 and chalcedony have been used from the most ancient times 

 as articles of adornment and jewelry. The parti-colored 

 bands of the onyx furnished suitable media from which to 

 produce fine effects in relief and intag-lioengraving,in many 

 instances several bands of different colors being utilized 

 for this purpose. In modern times the skill of the glass- 

 maker has largely supplemented that of the engraver. — J. 



D. MALLONrCIO. 



Section of Jade. — Jade is not a mineral species, but its 

 name is given to various minerals having a similar charac- 

 teristic physical structure which makes the material ex- 

 ceedingly tough and therefore well adapted for the manu- 



