HYDRATES AND CARBONATES OF THE ALKALI-METALS, ETC. 



459 



Hence by calculation — 

 Carbonic acid, 

 Oxide of sodium, Na 2 0, 

 Water, by difference, . 



I. 



. 40-648 



. 59-204 



0-148 



II. 



40-765 



59-238 



-0-003 



Mean. 



40-706 



59-221 



0-073 



100-000 



100-000 



100-000 



The 0'073 per cent, of water maybe put down as an observational error ; if we do so, 

 and calculate all the Na 2 not carbonate as Na 2 0, we have : — 



Carbonate of soda, 

 Oxide of sodium, 



98168 

 1-759 



99-927 



This experiment clearly shows, that at the temperature at which it was made (which, 

 according to a direct trial with beads of the metals, lay somewhere between the fusing- 

 points of gold and silver), carbonate of soda does suffer dissociation to a very ap- 

 preciable extent. And, as the temperature which prevailed in those experiments which 

 were made in a directly heated platinum crucible, must have been higher, we must 

 presume that in these also, the reaction Na 2 C0 3 + H 2 == 2NaOH + CO was accompanied 

 by a simple decomposition of carbonate into oxide and carbonic acid. 



From Scheerer's results (see p. 440) it would appear that the dissociation-tension of 

 carbonate of soda has an appreciable value even at temperatures not far above the fusing- 

 point of the salt ; but it is not likely at such temperatures to come up to one atmosphere. 

 So I thought, and to test my presumption, made the following experiment : — 



Experiment (11). — About 4 grm. of carbonate of soda (prepared from pure oxalate) 

 was fused in a platinum crucible by means of a powerful Bunsen, and kept over this 

 lamp for three hours, while a current of dry carbonic passed through the crucible. 

 The carbonic acid was stopped shortly after the lamp had been withdrawn, and the 

 contents allowed to freeze. The percentage of carbonic acid was determined twice with 

 the following results : — 



Mean. 





I. 



II. 



Substance taken, 



. 1-2244 grm. 



1-9493 grm. 



Carbonic acid obtained, 



. 0-5112 



0-8093 



Percentage of C0 2 , 



. 41-75 



41-52 



41-63 



Pure carbonate of soda by calculation contains 41 '466 per cent. To another 

 preparation subsequently made, the chloride of barium method for the determination of 

 caustic alkali was applied by Mr Henderson, who obtained a negative result, although, 

 according to his own synthetical results, less than 0*05 per cent, could easily have been 

 detected. (Compare results given on p. 454.) Our preparation clearly was pure normal 

 Na 2 C0 3 . It differed markedly from the ordinary preparation ; while the latter is very 

 decidedly hygroscopic and perfectly opaque, our salt was almost transparent like glass, 

 and devoid of all hygroscopicity. It struck me that carbonate of soda fused at the 



