Chenustry and Physics. 343 
the pressure can be calculated at which the one variety should be 
converted into the other. The value deduced is 34,000 atmo- 
spheres, on the supposition that the compressibility does not vary, 
and this not being strictly true, the required pressure in fact 
would be still greater or beyond the limit of experiment. The 
author, however, has found it possible to prepare a form of black 
sulphide differing less from the red in density. By subliming 
mercuric sulphide under ordinary conditions the red crystallized 
variety is formed, but if the vapors are diluted with a sufficient 
volume of inert gas (as CO,, or N), a black powder is obtained 
containing black opaque crystals quite distinct from cinnabar and 
also distinct from the black variety obtained by precipitation. 
This variety was found to have a specific gravity of 8°0395 and a 
specific volume of 124°385 at 17°. For this a pressure of about 
2,500 atmospheres, which it is easy to obtain, suffices to convert 
it into the red sulphide; the black sulphide being changed 
throughout its mass to the red vermilion. Finally the author 
finds that while the red sulphide if heated at 250° begins to turn 
black but assumes its red color on cooling, and while this is true 
up to 320°, if heated above 320°, it remains black permanently; 
this is then a critical temperature above which the red variety 
ceases to exist.— Bull. Acad. Roy. Belgique, II, xxviii, 238-257. 
2. The color, density and surface tension of hydrogen perox- 
ide.—Recalling the observations of Bunsen that pure water has a 
bluish color in a layer 2 meters in thickness and in one greater 
than 7°5 meters a bluish green, W. Sprine states that his obser- 
vations show that the color does not change with the thickness 
of the layer, the shade only varies. He ascribes the green tints 
to a yellow fluorescence produced by the play of the white light 
upon minute solid particles in suspension. He also notes the 
observations of Olzewski that liquid oxygen shows a blue color 
in a thickness of 30™, Further, he remarks that ozone as a gas 
has also a blue color in a layer of 1 meter in thickness (Haute- 
feuille and Chapuis), while in the liquid form it is blue and almost 
opaque in a layer of 2™™ (Olzewski). The author has now shown 
that hydrogen peroxide, like oxygen, ozone and water, also has a 
blue color, though hitherto it has been stated to be a colorless 
liquid. With great care he has prepared a considerable amount 
of the pure material, viz: 212 grams representing some 140° at 
13°. Of this the specific gravity was found by means of a 
pycnometer to be 1:4996 at 1°°5, and the value of the surface 
tension, compared with that of water, was determined to be 
0-456. The color was observed in a tube 1 meter in length; this 
placed vertically showed, after the bubbles of gas had disap- 
peared, a distinct d/we color somewhat tinged with green; the 
green however is regarded as non-essential. A quantitative de- 
termination of the color showed that the tint, while similar to 
that of water, was deeper, the relation between the two being 
1:1°83; this was obtained by comparisons of each with layers of 
copper chloride of such thickness as to give the same tint. From 
