294 Prof, J. W. Mallet on the Chemical and 
resublimed, but it again collected of the same tint as before. It 
appeared to be even more fusible and volatile than osmic acid ; 
t took along time to congeal under a stream of cold water flow- 
ing over the outside of a tube in which it had been melted. 
The water in which it was fused acquired a bright yellow 
colour, and gave off fumes, the odour of which seemed to me 
somewhat different from that of osmic acid, and which irritated 
the eyes so insufferably that it was scarcely possible to finish 
work with the acid and put it up for preservation. It was re- 
moved as a single cake from the water, and sealed up hermeti- 
cally in a glass tube which had been previously cleansed with 
care from all traces of dust or other organic matter. The water 
in which it had been fused was mixed with caustic potash, and 
gave a solution of very dark brown-red colour, such a tint as 
would probably result from a mixture of the red* osmite of pot- 
ash discovered by Fremy with the orange-brown osmiate of pot- 
ash. 
The sealed tube containing the fused cake or stick of yellow 
acid was allowed to remain upon a table exposed to the direct 
rays of the sun. The acid immediately began to sublime upon 
the sides of the tube, not in long needles and prismatic crystals 
like osmic acid (which seems to be monoclinic), but in feathery 
crusts like sal-ammoniac, which under a lens had somewhat the 
appearance of minute octahedrons grouped together. The colour 
was still bright yellow, but in a short time the sublimed acid 
began to turn black, and in twenty-four hours the whole inner 
surface of the tube was perfectly black and opake. A tube 
containing pure colourless osmic acid has been exposed in a simi- 
lar way to the sun for three weeks without any such blackening 
taking place. A tube closed by a cork, or one from which dust 
has not been carefully removed, will often cause osmic acid to 
turn dark, but never exhibits anything like the absolute black- 
ness and opacity of the whole tube noticed in the present in- 
stance. 
It is easy, however, to imagine the cause of this change under- 
gone by the yellow acid if it be m fact the teroxide of osmium 
(mixed with osmic acid). The teroxide probably broke up into 
osmic acid, and one of the lower oxides of osmium, or perhaps 
the metal itself. We might have 
20s0?= OsO0*+Os0?, 
5 OsO®=8 OsO* + Os? 08, 
3 Os0?=2 Os0*+ OsO, 
or 4.0s0?=30s0*+ Os. 
* A yose-red colour is also characteristic of the salt supposed by Berze- 
lius to be the ammonio-terchloride of osmium, corresponding in the chlorine 
series to osmite of ammonia. 
