Scientific American Supplement, No. 520, December 19, 1885 | Page 6

soldered link and holding an open handkerchief
between the lamp and link. Though the handkerchief was not charred,
hot air enough had reached the metal to fuse the solder and allow the
apparatus to start into operation.
These solders are alloys more fusible than the most fusible of their
component metals. A few of them are: Wood's alloy, consisting of:
cadmium, 1 to 2 parts; tin, 2 parts; lead, 4 parts; bismuth, 7 to 8 parts.
This alloy is fusible between 150° and 159° Fahr. The fusible metal of
D'Arcet is composed of: bismuth, 8 parts; lead, 5 parts; tin, 3 parts. It
melts at 173.3°. We can, therefore, by proper mixture, form a solder
which will melt at any desirable temperature. Numerous devices for
closing doors automatically have been constructed, all depending upon
the use of the fusible solder catch.
* * * * *

STEEL STRUCTURES.
At a recent meeting of the Engineers' Club of Philadelphia, Mr. James
Christie presented a paper upon "The Adaptation of Steel to Structural
Work." The price of steel has now fallen so low, as compared with iron,
that its increased use will be actively stimulated as the building

industries revive. The grades and properties of the steels are so distinct
and various that opinions differ much as to the adaptability of each
grade for a special purpose. Hitherto, engineers have favored open
hearth steel on account of uniformity, but recent results obtained from
Bessemer steel tend to place either make on equality. The seeming
tendency is to specify what the physical properties shall be, and not
how the steel shall be made.
For boiler and ship plates, the mildest and most ductile steel is favored.
For ships' frames and beams, a harder steel, up to 75,000 pounds
tenacity, is frequently used. For tension members of bridges, steel of
65,000 to 75,000 pounds tenacity is usually specified; and for
compression members, 80,000 to 90,000 pounds. In the Forth Bridge,
compression steel is limited to 75,000 to 82,000 pounds. Such a marked
advantage occurs from the use of high tension 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 made in such a manner that other persons using
instruments similarly constructed would be able to obtain the same
results.
Perhaps the most important tests needed are in regard to the
sensitiveness of the plates. Most plate makers use the wet plates as their
standard, giving the sensitiveness of the dry plates at from two to sixty
times greater; but as wet plates vary quite as much as dry ones,
depending on