444 PROFESSOR W. DITTMAR ON THE BEHAVIOUR OF THE 



Experiments in Carbonic Acid. 



From our general experience regarding decompositions like the one under 

 consideration,* we have a right to presume that the decomposition of carbonate 

 of lithia at a red heat can be prevented by maintaining over the heated carbonate 

 an atmosphere of carbonic acid of sufficient density, and from the fact that in 

 the two (nitrogen) experiments quoted the carbonic acid came off only very slowly it 

 appears probable that even at a bright red heat the requisite carbonic-acid density, and 

 consequent carbonic-acid pressure, does not amount to much, perhaps to less than one 

 atmosphere? This idea formed the basis of the following experiments: — 



Experiment I. — A quantity of carbonate of lithia was placed in the gas crucible and 

 kept for an hour at a red heat, over an ordinary Bunsen lamp, while a current of dry 

 carbonic acid was made to pass through the crucible. The product, which had the aspect 

 of a dull-looking glassy fuse (a glassy structure or rather non-structure, is characteristic 

 for fused normal, in opposition to ordinary fused, carbonates of soda and potash — vide 

 infra), was tested in a roughly quantitative manner with chloride of barium, and found 

 to contain rather less than 0"2 per cent, of caustic lithia, Li 2 0. 



I here refer to a method for the detection and determination of caustic in carbonates of alkali, 

 which Mr Henderson worked out under my direction. A known weight of the carbonate is 

 dissolved in boiled-out water in a stoppered bottle, a sufficiency of boiled-out solution of chloride of 

 barium is then added, and the mixture allowed to stand in the absence of air, until the precipitate 

 has settled as far as possible. An aliquot part of the clear liquor is now drawn off {not filtered off) 

 and titrated with very dilute standard-solution of hydrochloric or sulphuric acid in the presence of 

 phenol-phthalein as an indicator. I prefer to fractionate gravimetrically, because this does not tie 

 one down to a pre-determined volume of mixture. By means of this method (which, by the way, 

 does not pretend to be absolutely original) we had no difficulty in detecting considerably less than 

 01 per cent, of caustic potash or soda in the respective carbonate ; and a solution of absolutely 

 normal carbonate {vide infra) always gave a perfectly neutral decantate. But when we proceeded 

 to test it quantitatively, with solutions prepared from known weights of normal carbonate, and 

 known volumes of recently-prepared standard-solutions of caustic alkali, the general result, at least 

 in all those cases in which the caustic alkali amounted to 1 per cent, or less, was that only some 

 two-thirds of the RHO passed into the barytic solution. I accordingly put down the method as 

 being exact only in a qualitative sense. But we subsequently came to use it frequently side by 

 side with the gravimetric method (determination of the C0 2 and of the total B 2 0), and always found 

 the two methods to give fairly agreeing results. Hence, in all probability, the caustic alkali 

 solutions used in the synthetical trials, all precautions notwithstanding, contained part of their 

 alkali as R 2 C0 3 . 



To give a more exact idea of the method as applied to carbonate of lithia, I may quote the 

 analysis of a carbonate " Q " which will be referred to below as an important preparation. 

 1-825 grm. of this substance was dissolved in about 300 c.c. of boiled-out water in a glass-stoppered 

 bottle standing over a water-bath. After all the carbonate had dissolved, which took a long time, 

 the solution was allowed to cool to almost ordinary temperature, and then mixed with recently 

 boiled-out solution of 10 grm. of chloride of barium. The bottle was then left to itself for about 

 twenty-four hours, when the precipitate had settled very well. The bottle was then weighed, when the 



* See my memoir on the "Oxides of Manganese" in the Proc. Roy. Soc. Edin., for 1864, also Chem. Soc. Jour., 

 same year, p. 294 ; also Debray's " Experiments on Carbonate of Lime," Jahresb. for 1867, p. 85. 



