54 Proceedings of the British Association. 



known resins divide 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 substance resembling coal, but which he 

 affirmed to be ulmic acid. He stated that the same substance 

 might be obtained from peat by digesting it in ammonia, and af- 

 terwards precipitating the brown solution by an acid ; while, on 

 the other hand, caustic potash extracts another acid, 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 

 a slight 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 

 placed on the glass, the lines will no longer be visible through 

 the microscope, until it is raised above the crystal three hundredths 

 of an inch. 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 a scale of hundredths of an inch, with a vernier dividing 

 it into thousandth parts. — Prof. Gregory communicated a paper on 

 the preparation oi alloxan, alloxantine, thionurate of amtnonia, ura- 

 mile, and murexide. 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 



