332 Scientific Proceedings, Royal Dublin Society. 



neutral solutions, is crimson in solutions of alkalfes and alkaline 

 carbonates, but it is also colourless in solutions of acid-carbonates. 



The test solution I use is made by dissolving 10 per cent, of 

 pure sodium acid-carbonate in distilled water. If this solution is 

 tested with phenol-phthalein, it will probably give a faint pinkish 

 coloration, although the sodium acid- carbonate may be perfectly 

 pure. The act of dissolving it produces a slight dissociation. 

 This coloration is indeed so slight that in practice it might be 

 ignored. I prefer, however, to gradually add a few drops of a 

 normal solution of nitric acid. After this treatment we get a 

 solution which is quite colourless when tested with phenol- 

 phthalein. If the sodium acid-carbonate solution has been laid by 

 for some time, it must be again brought to the neutral stage. 



Most metallic oxides, acting on this solution, will reduce a 

 certain proportion of the acid carbonate to the normal carbonate, 

 according to the following equation : — 



MO + 2NaHC0 3 = Na 2 C0 3 + M00 3 + H 2 0. 



I find that most of the hydroxides, and oxides formed in 

 the moist way, will bring about this decomposition. Those that 

 have been ignited do not, as a rule, act so well. 

 The test may be applied in two ways — 



(1.) A little of the suspected substance is rubbed in a mortar 

 with two or three c.cs of the sodium acid-carbonate 

 solution. It is then thrown upon a filter; and if it 

 contains any of the specified oxides, the filtrate will 

 immediately give a deep crimson coloration with the 

 phenol-phthalein solution. The object of rubbing in 

 a mortar is, that as we are dealing with insoluble oxides 

 and insoluble carbonates, the reaction is rather slow 

 unless this device is adopted. 

 (2.) If time is no object, it is not necessary to do this. The 

 suspected substance is shaken occasionally for about an 

 hour in a test-tube, when the decomposition will be 

 sufficiently advanced to give a marked reaction. On 

 testing the filtrate from such an experiment, heat 

 should not be applied. Dissociation of carbonic acid 

 takes place, resulting in permanent decomposition when 

 operating in an open tube. 



