It is as well to add a few drops of ammonia to the
last quantity of alcohol used.
The plate bearing the film negative is now placed in a warm locality,
under which circumstances a few hours will suffice for the complete
drying of the pellicular negative, after which it may be detached
with the greatest ease by lifting the edges with the point of a
penknife.--_Photo. News_.
* * * * *
NEW ANALOGY BETWEEN SOLIDS, LIQUIDS, AND GASES,
By W. SPRING.
The author asks in the first place, What is the cause of the different
specific gravities of one and the same metal according as it has been
cast, rolled, drawn into wire, or hammered? Does the difference observed
prove a real condensation of the matter under the action of pressure, or
is it merely due to the expulsion by pressure of gases which have been
occluded when the ingot was cast? According to well-known researches,
metals such as platinum, gold, silver, and copper, which have
been proved to occlude gases on fusion, and to let them escape,
_incompletely_, on solidification, are precisely those which are
most increased in their specific gravity by pressure.
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