144 CARNEGIE INSTITUTION OF WASHINGTON. 



laboratory conditions; comparatively few binary systems of the type water- 

 salt have been studied even up to their boiling-points and the interesting field 

 of higher pressures and temperatures up to and including the critical point 

 is almost untouched. 



The ternary system H20-K2Si03-Si02 has been studied over the temper- 

 ature range 200° to over 1000°. The work comprises a determination of the 

 composition and properties of the various stable solid phases which can coexist 

 with solution and vapor within the above temperature range, of the composi- 

 tion of the solutions in equilibrium with the solid phases, of the change in com- 

 position of these solutions vnth. temperature, and the approximate determina- 

 tion of the corresponding 3-phase pressures. 



The chief experimental method used was an adaptation of the "quenching" 

 method so extensively used in this laboratory for the investigation of dry 

 melts. The anhydrous components were heated in closed bombs with water to 

 the desired temperature, left until equilibrium was established, and quenched 

 by plunging the bomb into water. If the charge was all liquid, microscopic 

 examination of the solidified melt showed only glass; if the charge was a mix- 

 ture of solid and liquid, the microscopic examination showed a mixture of 

 crystals and glass. Depending on the result of the examination, more or less 

 water was added to a second charge and the process repeated. By this means it 

 was possible to fix the exact amount of water necessary to dissolve the material 

 completely. The microscopic examination revealed the solid phase with which 

 the liquid was in equilibrium ; the amount of water in the liquid was determined 

 from the difference in weight of the quenched hydrous glass and the anhydrous 

 materials originally used, and the pressure was calculated by means of van der 

 Waals's equation from the known amount of water in the vapor space at the 

 temperature of the experiment. 



The following are the compounds which occur: Silica, Si02; potassium 

 hydrogen disilicate, KHSi206; potassium disilicate, K2Si205; potassium disili- 

 cate monohydrate, K2Si205.H20; potassium metasilicate, K2Si03; potassium 

 metasilicate hemihydrate, K2Si03.^H20; and potassium metasilicate mono- 

 hydrate, K2Si03.H20. 



In the binary system H20-K2Si03, K2Si03 is stable solid phase from its 

 melting-point at 976° to the quadruple (transition) point, K2Si03.^H20- 

 K2Si03 at 610°. The composition of the solution at this point is 0.345 

 mol H2O, 0.655 mol K2Si03; the corresponding pressure is about 9 atmos- 

 pheres. K2Si03.^H20 is stable from 610° to the quadruple (transition) point 

 K2SiO3.H2O-K2SiO3.IH2O at 370°; the composition of the solution is 0.53 

 mol H2O, 0.47 mol K2Si03, and the pressure, 6.2 atmospheres. At a tem- 

 perature a little below 200°, K2Si03.H20 is decomposed by H2O. 



In the binary system H20-K2Si205, K2Si206 is stable from its melting-point 

 at 1041° to the transition (quadruple) point K2Si205.H20-K2Si205, at 410°; 

 the composition of the solution at the quadruple point is 0.628 mol H2O, 

 0.372 mol K2Si205, and the corresponding pressure is 36 atmospheres. At 

 about 280°, K2Si205.H20 is decomposed by H2O. 



Potassium hydrogen disilicate, KHSi206, has a congruent melting-point 

 at about 515°. It is decomposed by H2O below 400°. 



The various quintuple points, at which three solids can coexist in equilib- 

 rium with vapor and solution, are as follows: Quintuple point K2Si03- 

 K2Si03.|H20-K2Si206-L-V at 575° and a vapor pressure of 1.5 atm. ; quintuple 

 point K2Si03.|H20-K2Si208.H20-K2Si205-L-V, 350° and 2.4 atm.; quintuple 

 point K2Si03.|H20-K2Si03.H20-K2Si206.H20-L-V, 300° and 2.7 atm.; quin- 

 tuple point K2Si206.H20-K2Si206-KHSi206-L-V, at 405° and 32.3 atm.; and 

 K2Si205-KHSi205-Si02-L-V, at 510° and 12 atm. 



