MERCURIC SALTS CHANGE INTO EACH OTHER. 1 Q]^ 



oxidises in the air. In a closed space, in presence of air, it increases 

 in weight, for there is then no appreciable loss due to volatilisation of 

 mercury, while there is combination with oxygen. But exposed to 

 the open air in thin layers there is loss in weight, because then the 

 effect of volatilisation of mercury more than counterbalances that of 

 taking up oxygen. In a closed space the substance never becomes 

 yellow, because the mercury cannot volatilise. That oxidation always 

 goes on in air till finished is also shown by the fact that the residual 

 mercuric oxide weighs much more than 52 per cent, of the original 

 substance. Bruns and von der Pfordten (1888) have also observed 

 that mercurous oxide oxidises in the air and that the presence of 

 moisture in the air hastens the oxidation. I myself made a number 

 of experiments before I had read Barfoed's paper in full. A summary 

 statement of all the results will be of interest. 



Barfoed by exposing .523 gram for a month in a bell jar 

 standing over water observed an increase of weight equivalent 

 to .067 per cent, per diem. That represents the oxygen taken 

 up under very favourable conditions and no material loss of 

 mercury. 



Bruns and von der Pfordten exposed 5.7635 grams to the 

 air for 12 hours only and observed an increase of weight equal 

 to .32 per cent, per diem (24 hours). This represents the dif- 

 ference of the gain in oxygen and loss in mercury. The same 

 chemists exposed 10.85-13 grams in a desiccator for 48 hours, and 

 observed an increase equal to .085 per cent, per diem, an in- 

 crease somewhat larger than Barfoed got as the average increase 

 a day, during a month in moist air. In this experiment there 

 will have been no material loss of mercury. 



I exposed, in cold dry weather, in an open porcelain 

 crucible for 15 days, 5.1037 gram, weighing every two days 

 about. The average increase in weight per diem was .025 per 

 cent., and the rate of increase, though not very regular, was 



