DECOMPOSITION OF HYDRIODIC ACID. CREIGHTON. 



Table VI. 



17 





No. of cc. of j^ Nrj Sa Og solution required in 







titration when the decomposition of hydriodic 





Temper- 

 ature. 



acid takes place in the dark in presence of 



Difference. 





No radium. 



Radium. 









0.20 



0.78 



0.58 



4 



0.45 



1.02 



0.57 



8 



0.68 



1.21 



0.53 



12 



0.95 



1.43 



0.48 



16 



1.20 



1.73 



0.53 



20 



1.25 



. 1.75 



0.50 



24 



1.23 



1 73 



0.50 



36 



0.93 



1.65 



0.72 





Mean of all Differences except that for 36°C. . . 



0.53 



If these numbers are plotted it is seen that the curves are 

 straight lines below 16°C. If the latter are produced backward 

 they will cut the axis of temperature at about — 12''C. and 

 — 3°C. for the radium and no radium curves respectively. At 

 these temperatures there should be no decomposition unless the 

 curves should become asymptotic, and, considering the steepness 

 of the curves at 0°C., this would not seem probable for the "no 

 radium " curve at least. Of course it was out of the question 

 to keep the solution at — 12°C. on account of its freezing, but 

 a solution could easily be kept at — 8°C. for a time. 



This temperature ( — 3°C.) was easily obtained by placing the 

 solution in a bath of very dilute alcohol, which was surrounded 

 by a mixture of salt and snow. It required but little attention 

 to keep this bath at a temperature of about — 3° 6C. to — 4°C. 



It was found at the end of ten hours that the decomposition 

 in a solution not under the influence of radium, and kept at a 

 temperature of — 3 °C. during that time, was equivalent to 

 0.19 cc. sodium thiosulphate. Hence the curves at CC. must 

 cease to be straight lines, and begin to run asymptotically 

 toward the axis of temperature. 



Proc. & Tkans. N. S. Inst. Sci., Vol. XII. Trans. 2. 



