172 



S. HADA; HOW MERCUROUS AND 



In a third experiment the mercurous nitrate was heated to 150° 

 with water only, for five hours, in an atmosphere of carbon dioxide. 

 It underwent no change beyond slight dissociation. Dissociation in a 

 sealed tube is impeded by the retention of the mercury vapour. Very 

 different was the result in an atmosphere of carbon dioxide when a 

 little nitric acid had been added, as will presently be described. In 

 the above cases, the nitric acid may have assisted as a carrier of the 

 gaseous oxygen, but as other mercurous salts are also oxidisable 

 at 150°, this possible assistance may be left, out of considera- 

 tion. 



Mercurous nitrate not sensibly oxidised by air at lower temperatures. — 

 In the experiments exhibiting the dissociation of mercurous nitrate at 

 100° and even a little higher, any oxidation by the passing current of 

 air did not betray itself ; for as much mercuric nitrate was produced 

 in a current of carbon dioxide or an atmosphere of steam. Also, at the 

 common temperature, in the dark, a. solution of mercurous nitrate 

 remains unchanged even in an atmosphere of oxygen. But, since 

 experiments made long ago by Mialhé have been accepted as establish- 

 ing the oxidizability of wet mercurous chloride by air at only a slight 

 elevation of temperature, it will be well to give the result of a 

 modification of his experiment, applied in such a way as to test the 

 point in the case of mercurous nitrate. His method consisted in 

 comparing the changes that went on in a closed vessel with those in 

 an open vessel in a current of air, while his results were the produc- 

 tion of much more mercuric salt in the latter case. The experiments 

 now to follow were hardly necessary, because Mialhé's results are only 

 in accordance with the occurrence of dissociation, but it seemed well to 

 make them. 



Two small flasks were provided and into each were put 1.5 

 grams mercurous nitrate and 15cc. water. One flask was closed by 



