ension steel in compression
members, and the danger of sudden failure of a properly made strut is so
little, that future practice will favor the use of hard steel in
compression, unless the material should prove untrustworthy. In columns,
even as long as forty diameters, steel of 90,000 pounds tenacity will
exceed the mildest steel 35 per cent., or iron 50 per cent., in
compressive resistance.

The present uncertainty consists largely as to how high-tension steel
will endure the manipulation usual with iron without injury. A few
experiments were recently made by the writer on riveted struts of both
mild and hard steel, which had been punched, straightened, and riveted,
as usual with iron, but no indication of deterioration was found.

Steel castings are now made entirely trustworthy for tensile working
stresses of 10,000 to 15,000 pounds per square inch. In some portable
machinery, an intermittent tensile stress is applied of 15,000 pounds,
sometimes rising to 20,000 pounds per square inch of section, without any
evidence of weakness.

* * * * *

Equal volumes of amyl alcohol (rectified fusel oil) and pure concentrated
hydrochloric acid, shaken together in a test tube, unite to form a single
colorless liquid; if one volume of benzine (from petroleum) be added to
this, and the tube well shaken, the contents will soon separate into
_three_ distinct colorless fluids, the planes of demarkation being
clearly discernible by transmitted light. Drop into the tube a particle
of "acid magenta;" after again shaking the liquids together, the lower
two zones will present different shades of red, while the supernatant
hydrocarbon will remain without color.

* * * * *

A METHOD OF MEASURING THE ABSOLUTE SENSITIVENESS OF PHOTOGRAPHIC DRY
PLATES.

[Footnote: From the Proceedings of the Academy of Arts and
Sciences.--_Amer. Jour._]

By WILLIAM H. PICKERING.

Within the last few years the subject of dry plate photography has
Increased very rapidly, not only in general popularity, but also in
importance in regard to its applications to other departments of science.
Numerous plate manufacturers have sprung up in this country as well as
abroad, and each naturally claims all the good qualities for his own
plates. It therefore seemed desirable that some tests should be made
which would determine definitely the validity of these claims, and that
they should be mad