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y occedings of the British Association 
<r resins aivide themselves into two groups, possessing un- 
like chemical and physical properties: of one, colophony is the 
~ type, and of the other gamboge, or dragon’s blood.—Prof. John- 
ston exhibited some varieties.of peat from the moss near Paisley, 
which he said illustrated a transition from the comparatively fresh 
vegetable matter to a substanee resembling coal, but which he 
affirmed to be ulmic acid. He stated that the same substance 
might be obtained from peat hee.” 4 it in ammonia, and af- 
terwards precipitating the brown. solution by an acid; while, on 
the other hand, caustic task ‘extracts another mid which he 
proposed to term humic acid. —Mr. Alex. Bryson stated a new 
method of ascertaining the, refractive powers of minute bodies, 
and its application to mineralogy. In ascertaining the refractive 
powers of crystalline substances, it is commonly thought neces- 
sary to procure pieces not less than a quarter of an inch in size, 
which are then to be ground into prisms. The microscope, with 
_aslight alteration, is well suited to give minute differences in re- 
fractive powers. On the stage of the microscope is placed a piece 
of crown glass, with fine lines drawn on its first surface. If a 
piece of beryl, or any other mineral with parallel sides, is now 
aced on the glass, the lines will no longer be visible through — 
the microscope, until it is raised above the crystal three hundredths 
of aninch. The difference of focus becomes an index of the 
difference of refractive power between the glass plate and the 
crystal. ‘The means adopted to ascertain minute changes in focal — 
‘length, is ascale of hundredths of an inch, with a vernier dividing 
wii into aeeemnits parts. ar tbh Seager communicated a paper on 
‘ ’ te of ammonia, ura- 
eal ad wmcatides To prepare alloxan from uric acid, Liebig and 
Wohler used nitric acid of sp. gr. 1.42, and separated the acid liq- 
uid from the crystals by means of a porous brick, thus losing the 
whole of the mother liquid. ‘The author uses nitric acid of sp. 
gr. 1.35. The action of this acid on uric acid must be kept mode- 
rate. When crystals of alloxan are formed, the whole is thrown 
on a filter, the throat of which is stopped with asbestus. ‘That 
portion of the acid liquid which remains in the crystals is displa- 
ced by a few drops of cold water, and the crystals are purified by 
recrystallization. The liquid is again employed in the same way 
and the crystals collected as before. Five such operations may 
be performed with the same liquid, each yielding a large crop of 
me 
oe 
