292 g - HADA; HOW MERCUROUS AND 



not less near the end of the exposure than on the first days. 

 I exposed in cold, dry weather, in a crusible for 17 days, 

 6.9874 grams. This time the rate of increase varied but little 

 from first to last, and was equal to .023 per cent, per diem. Tn 

 this and the previous experiment the result represented the 

 joint effect of gain of oxygen and loss of mercury. 



I spread moist over a glass dish, what when dry weighed 

 .840 gram. In a desiccator, it decreased in weight, but only 

 .001 per cent, in 13 days, which seems to prove that mercurous 

 oxide does not oxidise in dry air. The same portion was then 

 exposed to cold dry air for 14 days, during which time it lost 

 in weight at the rate of .004 per cent, per diem, as the combined 

 result of loss of mercury and gain of oxygen. The oxidation 

 of mercurous oxide is, therefore, a very slow process. So far 

 as can be ascertained, this oxide is the only mercury compound 

 that does oxidise at the common temperature, or even at 100°. 

 Mercurous carbonate is formed when moist mercurous oxide is 

 exposed to carbon dioxide gas (Barfoed). In the air, it slowly decom- 

 poses into carbon dioxide, mercury, and mercuric oxide. 



Non-existence of mercurous sulphide. 



When a solution of mercurous nitrate is added to one of potassium 

 cyanide, it is well known to produce a precipitate of half its mercury 

 as metal and to form mercuric potassium cyanide in solution. When 

 mercurous nitrate is added to excess of hydrogen sulphide, it is 

 represented by nearly all English authorities (I do not know an ex- 

 ception) to yield mercurous sulphide which begins at once to decompose 

 and, therefore, becomes a mixture of mercurous and mercuric sulphides 

 with metallic mercury. Yet, so long back as 1863, Barfoed submitted 

 satisfactory proof that hydrogen sulphide behaves like potassium 

 cyanide in at once converting a mercurous salt into mercury and 

 mercuric sulphide, and, therefore, that mercurous sulphide has no more 



