A direct transformation of one modification into the other has not yet
been accomplished. The effect of the light upon these substances is
incipient reduction, and we might hence suppose that the more reducible
indigo sensitive variety would be the more sensitive to light. But
this is not the case, because it is not chemical reducibility, but the
absorption power for light that is of the greatest importance. Now the
blue sensitive silver bromide has a greater absorption power than the
indigo sensitive variety, and hence its greater sensitiveness. Silver
chloride prepared by methods similar to those used in making the two
forms of bromides was also found to exist in two modifications. One is
designated as ultra violet sensitive, the other as violet sensitive
silver chloride.--_Amer. Chem. Jour_.

* * * * *




ANALYSIS OF A SAMPLE OF NEW ZEALAND COAL.

[Footnote: Read before the Society of Public Analysts on the 28th June,
1883.]

By OTTO HEHNER


Some discussion having recently taken place as to the value of New
Zealand coal as a fuel, the following results of a somewhat full
analysis may be worthy of being placed on record.