on the BoroAes of Bariicm. 55 



and the carbonate of barium is stable, or rather the temper- 

 ature at which it becomes stable." All these experiments, 

 and those in which the mixtures were exposed to the air and 

 dried in a dessicator, prove nothing ; in fact, Morse and Horn 

 only draw inferences from them (page 13i) : " From this it 

 appears probable that the more basic borate which is formed 

 at high temperatures, is decomposed at ordinary temperatures 

 by the carbon dioxide of the air and reconverted into the 

 borate and carbonate. A similar absorption of carbon dioxide 

 takes place when material whose weight has been reduced 

 below the normal amount, is reheated in the bath at temper- 

 atures under 500° C. From this it is inferred that normal 

 weights could be qiiicldy obtained by first heating to a high 

 temperature and then at a lower one, but we have not jet 

 tried the experiment." 



Those final and satisfactory weights which are sometimes 

 obtained may be due to the presence of an excess of carbon 

 dioxide or water, or both, in an amount sufficient to replace 

 any boric acid volatilized in evaporation and especially with 

 the water of hydration. That Morse and Horn did have 

 present in these experiments at the beginning of evaporation 

 some free boric acid — or, if it is preferred, a more acid borate — 

 and a corresponding increase in the amount of carbonate, is 

 certain, because in all these experiments of which the results 

 are recorded, carbon dioxide was passed for not less than 

 fifteen minutes, or when phenol phthalein was used as an indi- 

 cator, usually for five minutes after the disappearance of the 

 alkaline reaction. 



In my original paper I suggested the use of phenolphthalein 

 to prevent too great an excess of carbon dioxide and corre- 

 sponding decomposition of the metaborate. In a recent experi- 

 ment I have tested the action of a metaborate in alcoholic 

 solution upon this indicator, and find that exact equivalents of 

 barium hydrate and boric acid in 78 per cent alcohol give a 

 decided alkaline reaction, and that this alkaline coloration dis- 

 appears only when about 36 per cent more boric acid is added. 

 It is clear that phenolphthalein gives indication, not when the 

 excess of barium hydrate is converted into carbonate, but at a 

 point considerably beyond. Morse and Horn, then, were 

 working with barium carbonate and an acid borate, and in 

 many cases, most certainly, with barium carbonate and free 

 boric acid. 



If by accident — and I see no other way of doing it — the 

 action of carbon dioxide is stopped just when the excess of 

 barium hydrate has been converted into carbonate, still noth- 

 ing is gained ; for the experiments of Morse and Horn — if 



