, Mr Hcrschel on the IlypomlphuronH Acid. 521 
a minute object under a microscope separates the two pencils in 
the direction of its longer diagonal. This salt has a great ten- 
dency to form macled or hemitrope crystals, being interrupted 
parallelepipeds, composed of two of those above described, joined 
by the edges of 97® 13', so as to have their adjacent faces on an 
exact level ; and, when this is the case, they separate readily at 
the juncture, the fracture being a perfect and highly polished 
plane. This tendency to form hemitrope crystals I have ob- 
.served in other salts. In nitre, it is even rare to meet with an 
hexagon free from this inversion of structure, which is not dis- 
coverable on external inspection, but manifests itself by certain 
optical phaenomena of extraordinary splendour, which I shall 
take some future opportunity to describe, and which may possi- 
bly indicate some yet unnoticed property of polarized light. 
This salt is soluble in about 4 times its weight of cold water 
(45®) and 1| of hot. Its taste is purely bitter. It is insoluble 
in alcohol, unless very dilute, and is in consequence precipitated 
by it from solution in water, in scaly crystals. Like the rest 
of the hyposulphites, it readily dissolves muriate of silver, and 
alcohol precipitates the solution in a sweet syrup. Heated, it 
whitens without losing its figure, and burns with a very faint 
flame. 
HyposulpliHe qf salt may be formed very 
readily by boiling a solution of sulphite of magnesia with flow- 
ers of sulphur. It is intensely bitter, but, though very soluble 
in water, apparently not deliquescent. Being much more so- 
luble in hot than in cold water, it readily crystallizes in cool- 
ing. Laid on a hot iron, it burns with a weak blue flame, but 
is incapable of maintaining the combustion per se. Heated in 
the flame of a blowpipe, it swells into a fungous mass, by the 
escape of sulphur, just as borax does by that of water. Pure 
magnesia remains soluble slowly and silently in acids. 
Hyposulphite of Alumina . — I should pass over this salt, which 
I endeavoured to insulate in various ways without success, but 
for a fact of some moment observed in the attempt. The mode 
wliich seemed to promise best, was to precipitate hyposulphite of 
lime by oxalate of alumina ; but, to my great surprise, on mix- 
ing the two solutions, though perfectly neutral, not the slightest 
cloud was produced. This singular suspension of one of the 
