478 J. 31. Ordway — Waterglass. 



a temporary precipitate ; but ammonia has a more lasting 

 effect. 



The ammonia water used in the following trials was of 

 sp. gr. 0-900. 



19. 40 cc of ammonia water mixed with 50 g. of a 29 p. c. 

 solution of 3Na 2 0-llSiO„ gave a curd weighing 16*8 g. and show- 

 ing 43 p. c. of 5Na 2 0-l7Si0 o . 



20. 50 g. of a 21 p. c. solution of 5Na 2 Ol9Si0 2 with 40 cc 

 of ammonia water threw down a cake containing 40 p. c. of 

 Na„O4Si0 2 . 



21. 20 g. of a 31 p. c. solution of 10K 2 O-33SiO 2 gave 6-2 g. of 

 cake containing 54 p. c. of 10K„O-38SiO o . 



22. 40 g. of K„0-3Si0 2 with 50 cc of ammonia water afforded 

 a 3 g. cake containing 55 p. c. of K„O4Si0 2 . 



23. 50 g. of a 9 p. c. solution of Li„Si0 3 with 30 cc of ammo- 

 nia water made a 4*3 g. cake with 44 p. c. of 3Li 2 04SiO„. 



24. 50 g. of a 33 p. c. solution of 10Rb„O37Si0 2 with 30 cc 

 of ammonia water produced a cake weighing 10 g. and contain- 

 ing 23 p. c. of 10Rb 2 O44Si0 2 . 



25. 15 g. of a 45 p. c. Rb 2 O9Si0 2 and 15 cc of ammonia 

 water gave 9*7 g. of thin liquid precipitate. Evaporated to 7*2 g. 

 it became very thick and almost solid. It then contained 70 

 p. c. of 5Rb 2 Ol2Si0 2 . 



In summing up results it appears that while the solubility of 

 the silicates of sodium, potassium and rubidium is unlimited 

 the lithium silicates have each its definite point of saturation, 

 and the monosilicate is less soluble than the more silicious ones. 



Simple lithium silicate solutions give precipitates when 

 heated which are mostly redissolved on cooling. 



Hence to concentrate weak solutions we must resort to 

 spontaneous evaporation in di*5 r air or in a vacuum. 



So, too, we cannot expect to obtain the hydrates by boiling 

 the anhydrous silicates in water. 



Combinations of lithium silicates with those of the other 

 alkaline metals when precipitated by heat or by other means 

 are not dissociated, though the composition is changed some- 

 what. 



The composition of soluble rubidium silicates, like that of 

 potassium waterglass, may vary infinitely between the propor- 

 tions of one equivalent of silicate, one equivalent of rubidium 

 oxide and nine of silicic acid to two of base. 

 . With lithium silicates the range is not so great. 



Ammonia may give precipitates with strong solutions of all 

 the more silicious of all silicates. 



Sometimes when lithium-bearing precipitates are dissolved 

 there is a residue which makes much show but really weighs 

 very little. 



