350 OXYGENATED COMPOUNDS OF CHLOKINE. 



gives rise to a liberation of heat of -f 3 '5, for the same weight 

 of oxygen. 



These relations are the more remarkable in the acids of 

 chlorine, since the formation of successive combinations of one 

 and the same element with oxygen generally liberates heat, as 

 is shown by the history of the oxygenated combinations of 

 sulphur, selenium, phosphorus, arsenic, etc. 



12. Nevertheless, similar anomalies are found in the study of 

 the combinations of iodine and nitrogen with oxygen. In fact, if 

 we compare hypoiodous, iodic, and periodic acids, J [I 2 + -f- 

 water = I 2 (in solution)] absorbs, according to the author's 

 experiments, a quantity of heat notably superior, in absolute 

 value, to 5*2. 



*[L + O fi + water = L0 5 (dissolved)] liberates ... + 21-5 (Thomsen) 



or ... + 22-2 (Berthelot) 

 i[I 2 + 7 + water = I 2 7 (dissolved)] liberates ... + 13-5 (Thomsen) 



Hence it is seen that the heat liberated presents a minimum 

 and a maximum, neither of which corresponds to the highest 

 degree of oxidation. The combinations of nitrogen and oxygen 

 present an analogous minimum for nitric oxide (p. 84). These 

 numbers are given here in order to show how difficult it is to 

 generalise the relations between the quantities of heat disengaged 

 or absorbed, and the multiple proportions of the successive 

 combinations of two elements. 



If the minimum of heat liberated or the maximum of heat 

 absorbed corresponded in all cases to the first term formed by the 

 successive union of two elements, and if the heat liberated then 

 increased regularly with the proportion of the variable element, 

 it might be supposed that one of the elements the one con- 

 sidered as constant undergoes a special isomeric modification 

 preceding the combination, and from which, as a starting-point, 

 the quantities of heat should be reckoned. But it seems 

 difficult to admit this hypothesis in the oxygenated series of 

 nitrogen, iodine, and even chlorine, series in which the thermal 

 minimum and maximum correspond neither to the first nor to 

 the second degree of oxidation. 



13. It was thought desirable to pursue the comparison 

 further, and to extend it to chlorous acid. To this end it was 

 attempted to prepare a definite salt, barium chlorite, which, 

 according to Millon, should be a crystallised salt. By closely 

 following the author's instructions, a crystallised salt was 

 obtained, presenting a scaly appearance as he says and 

 giving by analysis numbers which essentially correspond to the 

 formula Ba(C10 2 ) 2 ; but a closer examination showed that the 

 salt was nothing but a mixture of barium chloride and per- 

 chlorate in equivalent proportions (with a small percentage of 

 chlorite) 



BaCl 2 + Ba(C10 4 ) 2 . 



