116 PROCEEDINGS OP THE AMERICAN ACADEMY 



AgCl, AgBr, AgT. The solubilities of AgCl and AgBr are much 

 changed by continued shaking,* and I cannot 6nd that Goodwin has 

 taken this into account at all. I conclude, therefore, that if he had 

 shaken his AgCl and AgBr he would have found much smaller electro- 

 motive forces than those recorded in his paper. He has tried to prove 

 the accuracy of his formula in two ways. Having calculated the solu- 

 bilities by substituting the experimental data for the electromotive 

 forces in the formula, he reverses the operation, and, substituting the 

 solubilities, he calculates the electromotive forces. It is true that 

 there is an intervening step, but the principle is the same, also the re- 

 sult. If he had taken the cells AglAgNO;j|AgCl + KCll Ag, and 

 AglAgNO.^jlAgBr + KBr|Ag, and substituted directly in these, the fal- 

 lacy of such a test would have been patent. Instead of this he has 

 combined the two cells 



AglAgCl + KCll AgNOgl Agl AgNOgl AgBr + KBrl Ag = 



AglAgCl + KCllAgBr+ KBrlAg, 



calculated the electromotive force of the resultant cell, and compared 

 this with the experimental value and with the ditference of the mean of 

 the two component cells. Any other formula, which had given fairly 

 constant values for the solubilities, would have stood the test eqxially 

 satisfactorily. If, instead of taking Goodwin's formula and his value for 

 AgBr, 6.6 X lO"*^ reacting weights per litre, one takes, for instance, 

 ray first modification of his formula and the corresponding value for 

 AgBr, 31.5 X 10~" units, one will reproduce his table exactly. One 

 cannot agree with him when he says, in regard to this table : " Die 

 Uebereinstimmung der beobachteten mit den berechneten Werten ist 

 eine sehr gute, wie dem ja nicht anders sein konnte, wenn die frilhere 

 Formel (25), nach der die Loslichkeiten berechnet wurden, liberhaupt 

 richtig war. Sie bestjitigt also diese Formel." f The otiier proof is not 

 satisfactory in the light of my experiments. Goodwin determined the 

 solubility of thallium bromide by the electrical and by the analytical 

 methods, the difference between the two being about 10 per cent of the 

 total solubility. This result cannot be compared with the experi- 

 ments on the solubilities of the silver haloids, because the conditions 

 were not the same. In the thallium determinations the cell used was 

 of the form TllTIBr + KNOglTlBr + KBrlTI. There were bromine 

 ions in contact with both electrodes, while with the silver salts the 

 bromine ions only came in contact with one electrode. 



* These Proceedings, XXX. 385, 1894. 

 t Zeitsclir. f. ph. Ch., XIII. 651, 1894, 



