Intelligence and Miscellanies. 175 



it gave delicate and beautiful shades and exposed for weeks 

 to the direct rays of a midsummer sun, it remained uncdang- 

 ed. These properties induce me to recommend it as an ad- 

 dition to the number of pigments among which the artist 

 can make a choice. 



An economical process for preparing this salt, consists in 

 boiling a mixture of one hundred and twenty five parts of Io- 

 dine, and two hundred and fifty parts of clean fine iron filmgs, 

 with one thousand parts of rain water, in an oil flask. When 

 the brown color of the liquid, is succeeded by a light green, the 

 clear fluid is decanted and the residue washed with warm 

 water ; the washings being added to the green solution, two 

 hundred and seventy two parts of corrosive sublimate, dis- 

 solved in two thousand parts of warm water, are then added 

 to the former liquor and the resultmg precipitate, is after- 

 wards washed and collected. 



This salt either in crystals, or in powder, presents two dis- 

 tinct and beautiful colors. If the precipitate, obtained as 

 above, be heated in a small subliming apparatus, or in a glass 

 tube, it melts and sublimes copiously, and the vapor is 

 condensed in large transparent rhombic tables, of a fine sul- 

 phur yellow color. These crystals are permanent in the 

 air and unaltered by the direct solar rays ; but the slightest 

 friction, or the contact of a fine point, is sufficient to alter 

 their interior arrangement. The point of contact instantly 

 becomes of a rich scarlet and the same color spreads over 

 the whole surface if a single crystal, and extends to the most 

 remote angle, if a group of crystals be the subject of exper- 

 iment. This change of color is accompanied by a sensible 

 mechanical motion, so that a small heap of the crystals, ap- 

 pears as if animated. An ordinary electroscope does not 

 indicate the developement of any electricity, nor is there any 

 considerable elevation of temperature, during the change. 



By gently warmmg the crystals supported on paper over 

 the flame of a lamp, the original yellow coloured salt is ob- 

 tained, and the same experiments may be often repeated ; af- 

 fording an elegant illustration of the connexion between col-, 

 ors and the mechanical structure of bodies. Transparent, 

 but minute rhombic prisms of this salt, may be obtained by 

 allowing a hot solution of it, in a solution of corrosive sub- 

 limate to cool very gradually. 



A. A. Hayes, Roxbury Laboratory. 



