449 



to me that the entropy would undergo a modificalion through the 

 presence of some water as catalyst'). Before the publication of my 

 thesis for the doctorate Prof. Wegscheider led by slightly different 

 considerations, iiad pointed out that the explanation of Johnson's 

 experiment might among others he found by the assumption of two 

 modifications of the ammonium chloride''). When now Wallace's 

 paper came under m} notice, and I learned from it that ammo- 

 nium chloride shows enantiotropy, I have come to the conclusion in 

 connection with the above that I could investigate the possibility of 

 the explanation which Prof. Wegscheidkk considered the most pro- 

 bable. First of all J have repeated Wallace's experiments for this 

 purpose; it appeared to me already at the first thermical determina- 

 tion that really NH^Cl is enantiolropic, but that the temperature of 

 transition had to tieviate appreciably from the value given by 

 Wallace. In what follows I will begin with a description of the 

 experiments which I have carried out to define the point of transi- 

 tion of ammonium chloride as accui'ately as possible. 



3. Thermic detenninalioii of the point of iraiisition of nimno- 

 nium chloride. 



A test tube with ammonium chloride crystals was heated in an 

 oil bath at about 200°, and then placed on cotton wool in a wider 

 tube. Observation of the temperature every half minute showed the 

 temperature to remain constant at about 174°. If 1 placed a tube at 

 room temj)erature in the oiltiath of 200°, again in an air jacket, 

 then the temperature-time-curve appeared lo exhibit a horizontal 

 part abont 187°. Repetition of these experiments at lower tempera- 

 ture of the oil bath and with use of a second oil balh for the cooling 

 curves produced but little change in the temporary constancy of the 

 temperature. We must therefore deduce from these observations that 

 ammonium chloride possesses a [)oint of transition between 174° 

 and 187°, which is found too low on cooling and too high on 

 heating, through the conversion of the modifications proceeding too 

 slowly at the point of transition to consume the supplied heat im- 

 mediately and to supply the removed heat immediately again. The 

 point of transition could not be defined more accurately in con- 

 sequence of this retardation of the conversion. These experiments, 

 however, lead u)e to the conclusion that the temperature of 159°, 

 which Wallace gives for the point of fransitioti, is indeed, con- 

 siderably too low. 



1) KoHiNSTAMM ami ScHEFFER, Tliese Proc. XVII p. 789, (1!)10/11). 

 *; VVegsoheidek, Zeilschr. 1'. physik. Chemie. 65. 1*7 (1908). 



