FLUATES. 509 



6. The vapor, which rises, corrodes glass ; this effect is decisive 

 as to the presence of fluoric acid. 



7. Alkaline fluates deliquescent and difficult to crystallize. 



8. There are five native fluates , namely 



a.) Fluor-spar or fluate of lime the most important. 

 b.) The double fluate of soda and alumina, called the cryolite, 

 c.) The fluate of cerium. 



d.) The double fluate of cerium and yttria, and what some choose 

 to call 



(e.) The fluo-silicate of alumina the topaz. Turner. 



FLUATE AND BI-FLUATE OF POTASSA. 



1 . PREPARATION. FLUATE . 



(a.) Caustic potash and fluor spar do not produce this compound 

 by heat, but carbonate of potash and fluor do by double exchange. 



(b.) Water being added, the carbonate of lime is precipitated, and 

 the fluate ofpotassa is dissolved. 



(c.) Formed by saturating pure liquid fluoric acid with potassa,* 

 much heat is disengaged. 



2. PROPERTIES. 



(a.) JL gelatinous deliquescent mass, difficult to crystallize as- 

 sumes a foliated form if evaporation is pushed to dryness. 



(b.) Suffers the aqueous, and afterwards the igneous fusion, by 

 heat. 



(c.) Fluate of potassa acts upon silica and glass, especially when 

 aided by heat, and even spontaneously in the course of a day or two, 

 and a triple compound is formed of earth, acid, and alkali. 



(d.) The sulphuric acid expels the fluoric with brisk effervescence. 



BI-FLUATE. 



1. FORMATION AND PROPERTIES. This salt is readily formed by 

 leaving the acid in excess, and is easily converted into the neutral 

 fluate by heating it to redness, which expels one proportion of fluoric 

 acid. The bi-fluate crystallizes in square tables with the edges re- 

 placed ; it is very soluble in water. 



2. COMPOSITION. 1 proportion neutral fluate, and 1 of fluoric 

 acid; by ignition, it leaves 74.9 of neutral fluate, and the remainder 

 is composed of 11.5 of water, 13.6 acid.f 



* Or its carbonate. 



t Berzelius, Ann. ele Chim. etde Phys. Tom. XX VII. 



Addition to fluate of potassa. It is common in laboratories, to pass silicated flu- 

 oric acid gas through water ; gelatinous silica is deposited, containing fluoric acid, 

 and an acid fluate of silica remains in the water. If to this fluid, caustic potash, or 

 its carbonate, be added, there is formed an acid fluate of silica and potassa soluble 



