wa 
( 43 ) 
used the colorimetric method with litmus and phenolphthalein as 
indicators. 
As already stated, we got by a more accurate method the same 
surprising result as STARKE. When, however, we used instead of 
water containing carbon dioxide water, which was absolutely free 
from the same (obtained by passing air free from carbon dioxide 
for some hours through distilled water) we obtained just the opposite 
result and the NaOH solution always had a stronger alkaline 
reaction than the NaOQH—Na Cl solution, which agrees with the 
theory which requires, that the ionisation of the NaOH solution be 
repelled by addition of Na Cl. 
5. The explanation of the result obtained by STARKE is now as 
follows: 
On dissolving NaCl in distilled water a portion of the dissolved 
carbon dioxide is expelled, because the solubility of carbon dioxide 
in water is greater than its solubility in a solution of NaCl. 
Distilled water has, therefore, a stronger acid reaction than a solution 
of neutral NaCl!) in this same water and this stronger acid reaction 
of the water is so predominant that in STARKE’s experiment it 
exceeded the decrease of the ionisation caused by addition of Na Cl 
and thus caused that perplexing result. 
6. After obtaining the above result, we have tried to estimate 
the CO, in water and solution of salt colorimetrically by adding 
baryta water. Here we observed the peculiar phenomenon that, 
while the water became distinctly opalescent, this did not happen 
with the 15 percent solution of NaCl. Another experiment where 
we started from 100 cc. of water containing CO, to which was added 
100 cc. of a 15 percent solution of NaCl and then baryta water 
gave the same result; no opalescence was observed and it was not 
until the solution had been diluted many times with water con- 
taining CO,, that barium hydroxide caused a turbidity. A colorimetric 
estimation was, therefore, not possible in this manner. 
The explanation of this phenomenon must be found in the reversi- 
bility of the reaction 
1) It is plain that, if we want to find out the reaction of a salt, this should be 
dissolved in water absolutely free from carbon dioxide. We experienced the fact 
that NaCl, which was thought to be neutral on account of its neutral reaction in 
distilled water showed a decided alkaline reaction when dissolved in water free from 
carbon dioxide, 
