174 s - HADA; HOW MERCUROUS AND 



atmosphere of the tube ]iber;ite.s iodine from potassium iodide, and the 

 solution precipitated first by sodium chloride, and then by hydrogen 

 sulphide, is milky from sulphur. 



Mercurous nitrate changed by light to mercuric salt by redaction, of 

 nitric acid. — In a number of small Erlenmeyer flasks a freshly prepared 

 solution of mercurous nitrate dissolved in one per cent, nitric acid was 

 equally distributed, each flask receiving lOcc. solution containing one 

 gram of mercurous nitrate. Most of the flasks were exposed together 

 to strong day-light, the rest were kept in the dark ; other conditions 

 of the flasks varied, as will be described. Along with those exposed 

 to the light were others having the mercurous nitrate with water and 

 no nitric acid added. Some of the flasks had their contents examined 

 at the end of 19 days exposure ; the others at the end of 33 days. 

 The examination consisted in testing for nitrous acid in one tenth of 

 the solution by potassium iodide and starch, and for the quantity of 

 mercuric radical in the other nine-tenths, the mercuric sulphide being 

 washed successively with water, alcohol, and carbon bisulphide. The 

 air or other gas which the flask had been filled with at first, was found 

 apparently unchanged at the end. 



Under whatever other condition it had been, the mercurous 

 nitrate which had been exposed to light had in every case generated 

 much nitrous acid, and mercuric salt, while that which had been in. 

 the dark showed the presence of neither product in 19 days and only 

 insignificant amounts in 33 days. I believe none is produced ; for,. 

 I regret to have to admit, the darkness in which the flasks had been 

 preserved was far from being total. 



The difference between closed and open flasks was marked ; the 

 closed flask being closely sealed, the open one with its month under 

 only a cap of filter paper. In the closed flask the mercuric radical 

 was found to be half as great again in 33 days as in the open one. 



