342 proceedings: chemical society 



The 227th meeting was held at the Cosmos Club on Thursday, May 8. 



The following papers were read : 



H. C. Fuller, of the Institute of Industrial Research: The determi- 

 nation of caffein in tea and coffee. (Read by Mr. Wettengel.) The 

 method recommended by the author depends upon the separation of 

 the caffein from the body of the vegetable matter by means of acidu- 

 lated water, and its extraction from the decoction with chloroform. The 

 caffein is then purified by precipitation with iodin, the iodide is decom- 

 posed and the pure alkaloid finally extracted with chloroform. 



W. B. Hicks, of the Geological Survey: A short practical method for 

 the estimation of potassium. The method consists in the precipitation 

 of potassium by platinum chloride from the acidified solution, washing 

 with alcohol, solution in hot water, and reduction of the chlorplatinate 

 by metallic magnesium to obtain the platinum in a weighable form. 

 The method is applicable in presence of a variety of other salts, and 

 has been used by the author in the analysis of salines. 



Discussion. In reply to questions by Yoder and Grant, the speaker 

 pointed out that the presence of non-volatile salts would interfere with 

 the determination of the platinum by simple ignition. In reply to a 

 question by Seidell, it was shown that sodium chlorplatinate is dis- 

 solved out by alcohol, and does not interfere. 



R. C. Wells, of the Geological Survey: Quantitative relations between 

 oxidizing and reducing solutions. The use of oxygen and hydrogen elec- 

 trodes for measuring oxidation and reduction potentials in solutions, 

 such as ferrous and ferric solutions, is rendered possible by the use of 

 platinum. Acidity increases the oxidation potential, while alkalinity 

 increases the reduction potential. The degree of reproducibility of these 

 potentials was discussed. The oxygen and hydrogen potentials in pure 

 water can be calculated, as well as their change with the gas pressure, 

 and the two are found to become equal at 0.68 volt and at 10"^^ atmos- 

 phere. This potential marks the true boundary between oxidizing and 

 reducing solutions. Very nearly the same value is obtained by calcu- 

 lation from the known dissociation constant of water at high temper- 

 atures. 



Discussion. Blum inquired as to contact potentials in the liquid 

 circuit; these are small in comparison with the potentials measured. 

 Yoder inquired whether potential measurements could be used to deter- 

 mine acidity in soil solutions; this would be difficult in the presence of 

 oxidizing substances. Sullivan suggested an application to biochemi- 

 cal studies. Franklin inquired further as to the ferrous-ferric equilib- 

 rium. Blum stated that the hydrogen electrode has been successfully 

 used for determining acidity in materials such as vinegar and wines. 



H. C. Gore, of the Bureau of Chemistry: The hiocheinistry of the 

 banana. Experiments have been made on the ripening of bananas in 

 a respiration calorimeter and in humidors. During ripening the starch 

 decreases, reducing sugars and sucrose increase, and total solids decrease, 

 both in the pulp and peel. There is a considerable increase in the 

 amount of water in the pulp. The respiration rate reaches a maximum 



