in the Magnetic Field. 275 



with ferric chloride. Professor Ordway* has described very 

 similar variations in the reaction between nitric acid and iron. 



What may be termed the critical temperature, i. e. that at 

 which this change of reaction occurred, was found to be 40°. 

 Reactions in which the solution did not reach that tempera- 

 ture were accompanied by the evolution of hydrogen only, 

 while those in which this temperature was passed were of 

 the double character described by Ordway, the production of 

 hydrogen being followed by that of nitrous fumes. The dif- 

 ference between these reactions is best shown by curves. 

 Curves a, b and c, fig. 1, show the range of temperature during 

 three experiments in which the initial temperature was varied 

 within narrow limits for the purpose of determining the critical 

 temperature. The magnet was not in action during any of 

 these experiments, but in other respects the process was that 

 already mentioned. The curves show the temperature of the 

 solution as a function of the time. Ordinates denote tempera- 

 ture in degrees centigrade, abscissas time in minutes. The 

 curves "6" and "c" have two maxima, whereas "a" shows no 

 such peculiarity. The portion o w, of the curve o b, for ex- 

 ample, indicates the rise of temperature produced by the solu- 

 tion of the iron under conditions in which hydrogen alone was 

 generated. Whenever the solution reached the critical tem- 

 perature (40°), a second reaction followed, in which red fumes 

 were given off and a new rise of temperature occurred. The 

 higher the temperature reached during the first reaction the 

 more promptly the second one took place ; as may be seen 

 from the diagram. Curves "6" and "c" show the double reac- 

 tion, "a" represents one in which the critical temperature was 

 not reached and no nitrous fumes appeared. 



The first reaction made in the magnetic field, under condi- 

 tions which would otherwise have ensured the evolution of 

 hydrogen only, was marked by an almost immediate and violent 

 outburst of red fumes accompanied by a correspondingly 

 greater rise of temperature. The reaction was repeated many 

 times and always with the same result. The modification in 

 the reaction produced by magnetic influence may be seen by 

 comparing curve " o(," which represents the rise of temperature 

 when the reaction took place in the field with curve "a." The 

 speed of the reaction is much greater within the magnetic field 

 than without, and the amount of heat produced is greater. 

 The evolution of nitrous fumes and the yellow color of the 



*" Malleable iron in dilute nitric acid, sp. gr. 1 -03 to 1 '06, is attacked with, 

 elimination of hydrogen and the production of a ferrous salt or with elimination 

 of nitrous dioxide and the production of a ferric salt or without any evolution of 

 gas." '• Sometimes hydrogen is produced at first, then nitrous dioxide, when both 

 ferrous and ferric salts will be formed." Watts' Diet. (Supplement.) See also Ord- 

 way, this Journal, II, vol. xl, p. 316. 



