351 



H = О 3 6 9 



COo = 104.5 99.3 94.8 90.7 

 Difference 5.2 5.0 3.6. 



The water continued to give off carbonic acid, and Dittmar 

 clearly saw that this must must mean that the dissolved bicar- 

 bonate possesses a tension of dissociation. On p. 212 he calculates 

 the tension produced in the air, with which the water was 

 shaken, and find it to be 5.7, 5.5 and 3.9 ten-thousandths of 

 an atmosphere respectively ^). Though these figures indicate a 

 steady lowering of the tension Dittmar calculated their mean 

 = 5.0 and took this to be the tension of dissociation for the 

 bicarbonate present in his artificial seawater, irrespective of 

 the quantity of bicarbonate as compared with that of normal 

 carbonate. Dittmar was of opinion that, if the tension is only 

 kept below this value, the bicarbonate will continue to give off 

 carbonic acid, and he hoped «before long to be able to for- 

 mulate the exact conditions of stability in seawater-bicarbonates 

 as they exist when dissolved in real seawater, and amongst 

 others to decide the question whether in this process they 

 quite directly tend to become normal and do not perhaps more 

 directly gravitate towards the state of sesqui- carbonate» (op. 

 cit. p. 212). 



As will be seen from the following this view of the question 

 Is fundamentally erroneous. One of the two chief factors on 

 which the tension depends is the relation between the quantities 

 of bicarbonate and normal carbonate present in the solution ^). 



In Encyclopcedia Britannica (vol. 21 p. 612) Dittmar has 

 published some further experiments concerning the tension 



There must be an error somewhere in Dittmar's determination or 

 calculations. He seems to have forgotten that the shaking with 5 

 volumes of air was repeated thrice between every two determinations 

 of the quantity of carbonic acid. At least I find the tension in each 

 case to be exactly Чз of the value given by Dittmar. 

 The influence of the other factor, the temperature, was correctly recog- 

 nized by Dittmar. though he did not determine it experimentally. 



