02 Dr. A. R. Leeds on the Decomposition of Equivalent 



Influence of increased Supply of Oxygen. March 19, 1879. 

 11 A.M.-12. Feeble Sunlight. 



With oxygen. Without. 



H 2 S0 4 + KI . . . 7-15 2-9 



HOI + „ ... 10-60 4-3 



I so ivith Nitric Acid. 



1-2 P.M. 



Snowing at time. 



H 2 S0 4 + KI . . 

 HN0 3 + "„ . . 



. 5-25 

 . 6-75 



1-5 

 2-5 



The absorption of oxygen when sulphuric and hydrochloric 

 acids are employed is expressed by the equations 



(1) 4KI + 2H 2 S0 4 + 2 = 2K 2 S0 4 + 2H 2 + 2I 2 , 

 and 



(2) 4KI + 4HC1 +0 2 =4KC1 +2H 2 + 2I 2 . 



And since 100 cubic centinis. of water, when saturated with 

 air under the ordinary circumstances of temperature and pres- 

 sure, would hold in solution only about 1 mgrm. of oxygen, 

 the maximum amount of iodine which could be liberated du- 

 ring one of these tests, in case no fresh absorption of oxygen 

 took place from the upper surface, would be *16 mgrm. The 

 influence of these conditions upon the accuracy of the estima- 

 tions made with the iodo-acid actinometers is being submitted 

 to further investigation. 



In the case of nitric acid the reactions become much more 

 complicated. For, in the first place, of the three mineral acids, 

 nitric is the only one which spontaneously decomposes when 

 subjected to sunlight in closed vessels. This is true both of 

 the concentrated acids and when diluted with 500 times their 

 volume of water. Moreover, in the latter case the presence of 

 starch had no influence except in the nitric acid, in which it 

 nearly doubled the rate of decomposition. The same effect of 

 starch (whether it is true of organic matter in general has not 

 been determined) is to be noted in the above table of decom- 

 positions for March 18, in which it will be seen that in the 

 trials where starch was present the amounts of iodine liberated 

 by nitric acid were largely in excess of those set free by equi- 

 valent amounts of other acids. In fine, while nitric acid con- 

 forms to the general law of actinic change, as expressed by the 

 equation 



4KI + 4HN0 3 + 2 = 4KN0 3 + 2H 2 + 2I 2 , 



it is likewise subject to the special decomposition 



4 HNO3 (in sunlight) = 2 N 2 4 + 2 H 2 O + 2 . 



For these reasons, at an early stage of the inquiry, the actino- 



