468 PROFESSOR W. DITTMAR ON THE BEHAVIOUR OF THE 



hydrogen they lose carbonic acid with formation of oxide, R 2 0, or hydrate, RHO. In the 

 case of nitrogen, if contact of the substance with flame-gases be absolutely avoided, the 

 change proceeds very slowly. A product obtained from the soda-salt had the composition 

 Na 2 CO 3 + 0'0306 Na. 2 0. A product obtained from the potash-salt had the composition 

 K 2 C0 3 + 0-00673 K 2 0. 



In an atmosphere of hydrogen the decomposition goes further, with formation of 

 only hydrate, RHO. The most highly caustic products obtained had the following 

 compositions : — 



In the case of soda, Na 2 C0 3 + 0'3332 Na 2 O.H 2 0, or very nearly 3 Na 2 C0 3 + lNa 2 O.H 2 0. 



In the case of potash, K 2 CO 3 + 0*1134K 2 O.H 2 O ; or approximately 9K 2 C0 3 + 

 1K 2 0.H 2 0. 



These formulas, however, have a purely arithmetical meaning. We have no reason to 

 assume the existence of any such hydric carbonate as a chemical compound. That we 

 never obtained a residue consisting of unmixed hydrate is easily explained by the 

 relatively great volatility of the latter. Imagine, at a certain stage of the change, the 

 crucible contained x mgrm. of R 2 as carbonate and y mgrm. of R 2 as hydrate, then in 

 the next second, a small weight of fresh hydrate proportional to x will be produced, and 

 a small weight of the already formed hydrate proportional to y will be volatilised, so 

 that, at the end of that second we have x' mgrm. of R 2 as carbonate and y' mgrm. of 

 R 2 as hydrate, where, approximately at least, x' = x — Jcx and y' = y + kx — hy, where k 

 and h are constants whose meaning is obvious. The ratio x : y or the weight of R 2 

 present as carbonate per unit-weight of R 2 present as hydrate, passes from x : y to 



X ^ ™ d y> = y(l+Z*-h)- 



x' 



Supposing h is less than k, the denominator in the factor of — is greater than the 



numerator, x' : y' is less than x : y and this diminution will continue until at last the 

 carbonate present per unit of hydrate will be nil and the residue consist of pure hydrate. 

 This case is illustrated in our experiments on lithia, except that there the anhydride 

 Li 2 made its appearance. 



Supposing noiv h is greater than k, then, in the earliest stages of the process, k- is 



very great, so that the factor is less than unity ; the ratio x : y becomes less and less, 



but as it does so the denominator in the factor becomes less and less likewise and at 



last equal to 1 — k, and the ratio x : y becomes constant. This will occur as soon as x : y 



has assumed that value at which 



-.x 



or 



when 



k + k- - 



-h = 



= o, 



y 







Ml + — 



\ y 



■8- 



= o, 



x h 







y~k~ 



-i 





or 



