DETECTIOX OF ACIDS. 131 



fragment is not entirely dissolved, but remains 

 visible in the bead, retaining its original form. 

 Also, Y/hen the substance in powder is fused in a 

 bead of sodic carbonate on the platinum wire, the 

 bead froths, carbonic acid being set free. Both 

 these reactions together indicate Silicic. - - - 4 



4. A small portion of the original substance, finely 

 pulverized, is made into a paste with concentrated 

 sulphuric acid in a leaden tray, the tray is covered 

 with a piece of Bohemian glass coated with wax, 

 and from which the coating has been removed in 

 a few places with a sharp-pointed instrument, and 

 the whole is gently lieated for about a half an 

 hour. The glass is found to be corroded where 

 the wax was removed (see § G8). Fluorine. - 5 



5. The insoluble substance has black particles in it, 

 that are entirely or partially consumed when heat- 

 ed on platinum foil. (Coal.) Carbox. . - - 6 



6. Evaporate a portion of the first solution or of F 2 

 to dryness, after adding hydrochloric acid, if not 

 already present, ignite the residue gently, moisten 

 it with concentrated hydrocliloric acid, let stand a 

 short time, add considerable water, and digest the 

 mixture. A white poAvder, or perhaps a reddish 

 one if much iron is present, remains undissolved, 

 that feels gritty under the glass rod. Soluble 

 Silicic. - 'l 



7. The addition of dilute sulphuric acid to a small 

 quantity of the original substance causes efferves- 

 cence, that accompanies the evolution of a colorless 

 gas ; a drop of lime-water, suspended on the end 

 of a glass rod, and held above the liquid in the 

 test-tube, is made turbid. Carbonic. - - - - ^ 



6. In the same experiment a colorless gas is evolved, 

 having an offensive odor, and blackening a piece of 



