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Proceedings of the Royal Society 
and the water thickened into a soft crystalline mass. The quantity 
of the crystals depended on the amount of mercaptan if sulphuretted 
hydrogen were in excess, or on the amount of sulphuretted hydrogen 
if mercaptan were in excess. 
On cooling water saturated with mercaptan no such crystalline 
appearance was observed. As is known from Wohler’s experiments 
(Annalen der Chemie und Pharmacie, xxxiii. 125), sulphuretted 
hydrogen only forms a hydrate at -16°C., or under considerable 
pressure. Prom these results it is evident that both sulphuretted 
hydrogen and mercaptan are necessary for the formation of this 
crystalline compound. 
The crystalline mass has much the same appearance as hydrate 
of chlorine, but is colourless. In the mother liquid the crystals 
exist for an indefinite time at any temperature below 3°C.; when 
dried they rapidly melt even at 0° C. Above 3° C. they melt in the 
mother liquid, with evolution of sulphuretted hydrogen, and forma- 
tion of a thin layer of mercaptan above the water. Their specific 
gravity is greater than that of the mother liquid, which in turn is 
greater than that of ice. By allowing the crystals to stand in this 
mother liquid, in a corked flask cooled by means of ice-cold water, 
a crust forms on the surface, which appears to consist of hexagonal 
plates. 
Newly formed crystals when observed under the microscope 
appear to be prisms, some long and fine, others short and thick, but 
as they rapidly melt, their form could not be more accurately 
observed. They dissolve rapidly in absolute alcohol at - 10° C., with 
evolution of a little sulphuretted hydrogen. 
A mass of the crystals, when allowed to evaporate slowly, smell 
strongly of mercaptan, and deposit sulphur. Bapidly heated on 
platinum foil they suddenly melt, and a gas is given off which 
burns with a blue flame. The water left becomes milky with 
separation of sulphur. On further heat being applied the water is 
evaporated, and the sulphur burnt, without any residue. When 
dried between well-cooled filter paper, and dissolved in alcohol, 
with acetate of lead, a dark brown precipitate of sulphide of lead 
is thrown down, any precipitate of mercaptide of lead being hidden 
by the darker sulphide. 
The presence of mercaptan was distinctly proved by com- 
