M. Guillemin's Account of a Gelatinous Quartz, ^c. 825 



returned to their original state, that is to say, came to contain 

 only 11 or 12 per cent, of water. 



The density of a fragment saturated with water was 1.80 at 

 6i degrees, 1.812 at 6 degrees, 1.797 at 13 degrees; that of a 

 fragment containing 0.111 of water, 1,67 at 2 degrees; and 

 that of a dried fragment 1.53 at 5 degrees. In the two last ex- 

 periments, the absorption of water, and the disengagement of 

 gases were prevented, by covering the surface of the fragments 

 with a thin coat of olive oil. Lastly, the density of this sub- 

 stance, when weighed dry out of the water, and under the wa- 

 ter, after an absorption of eighteen hours, was found to be 2.215 

 at 13 degrees of the centigrade thermometer. 



Chemical Characters. — Exposed to the heat of a lamp in a 

 small matrass, this mineral affords water ; gently heated in a 

 platina crucible, it gives out all its water without losing its re- 

 sinous lustre ; it becomes a little more translucent, with a tint of 

 yellow opaline colour; when quickly heated, it decrepitates, 

 splits, whitens, and becomes opaque by the intrusion of the air 

 into the fissures which are formed. 



It is infusible before the blowpipe. The thinnest splinters, 

 when strongly heated, become transparent, and assume the vi- 

 treous lustre and hardness of hyaline quartz. It is affected, 

 like pure silica, with all the chemical agents. Caustic potash in 

 concentrated solution very readily attacks it at a boiling heat ; 

 it is dissolved almost instantaneously. Muriatic acid precipi- 

 tates it in large white gelatinous flakes, when the liquor is con- 

 centrated ; and, on the contrary, when a sufficient quantity of 

 water is used, a precipitate is not immediately obtained, and by 

 evaporation a transparent jelly is procured. 



Analysis — The water is not combined in this siliceous sub- 

 stance. I thought, at first, that it was ; having been deceived 

 by the difficulty of chasing the last pordons of this fluid, which 

 is experienced when the heat of boiling water only is employed ; 

 but, I found, that, by a pfrolonged desiccation, the water always 

 diminished, and at length was entirely expelled. The results 

 of its analysis are the following: 



JANUARY MARCH 1827. Y 



