THE SPEED OF REDUCTIONS 315 



other chlorides were mixed with ferric chloride to test their 

 effect upon its stability toward reducing agents. The method 

 followed closely that employed by A. A. Noyes, in studying 

 the speed of reaction between ferric chloride and stannous 

 chloride. He mixed dilute [602] solutions of these two salts 

 in equivalent proportions, drew measured samples from time 

 to time, running them into a solution of mercuric chloride, 

 to arrest the reaction by removing all the remaining stannous 

 chloride without affecting the trivalent iron; then determin- 

 ing the amount of the latter by titration with potassium 

 dichr ornate. Using twentieth normal solutions of these two 

 compounds, I obtained constants for the reaction agreeing 

 closely with Noyes's figures ; upon adding aluminic chloride, 

 also in twentieth normal concentration, the speed was more 

 than doubled; while it was quadrupled in the presence of a 

 tenth normal solution of aluminic chloride. Of course, such 

 a result might be ascribed to the excess of chlorine ions 

 present, especially as Noyes had found that hydrochloric acid 

 has an effect, though of a different kind. If so, chlorides of 

 divalent elements should not have so great an effect: yet 

 1/20 normal solutions of manganous chloride and of glu- 

 cinic chloride also double the speed of reduction, although 

 the ionization cannot be the same. A 1/20 normal solution 

 of quadrivalent thorium does not accelerate quite as much. 

 As is well known, Noyes considers this as a typical reaction 

 of the third order, and shows that his equation 



c = l ( l M 



2AU-.30 2 A 2 / 



applied to his experimental data, gives a fairly constant value 

 for Ca. My series, which I cannot reproduce in full, show about 

 the same degree of constancy for 3. Consequently, I think it 

 fair to assume that the reaction remains of the same type, 



