Pittsburg dispatch. [volume] (Pittsburg [Pa.]) 1880-1923, 1889-10-20
Leave. as Photographic Negatives.

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A remarkable discovery has just been
brought before the British Association by
Walter Gardiner in his paper on "a New
Method OF Printing Photographic Mega
tiVes, Employing Living Leaves in Place of
Sensitive Paper" Mr.. Gardiner stated
that whatever is the exact chemical nature
of the process, this, at least, is clear, that
the first visible product of assimilatory &C.
tivity is starch. which, moreover, is found in
the chlorophyll grains The presence of
this starch can be made manifest by treat
ing decolorized leaf with q water solution
OF iodine. This formation of starch takes
place only under the influence of light; the
radiant energy of the sun providing the
means of executing the synthetical
proteid from the carbonic acid of
the air which is taken up BY
the leaves and the salts and water absorbed
BY the roots. If plant (and preferably q
plant with thin leaves) be placed in the
dark over night, and then brought out into
the light next morning, the desired leaves
being covered with q sharp and we'll de-
veloped negative, starch is formed when
light is transmitted, and in greatest guam
tity in the brightest areas. Thus positive
in starch is produced which can be de-
veloped by suitable treatment with iodine.
Mr.. Gardiner showed that it might be pos
sible to obtain permanent print by suit
able washing and treatment with a soluble
silver salt, silver iodide being formed. He
regards this discovery as a most striking
illustration of the way in which plants are
IL 4, aaIr \ e.
things, and points out that the extraordinary
manner in which the green parts of plants.
so to speak, catch the radiant energy of the
sun, and employ it for analytical and syn
thetical chemical processes, may be easily
and clearly demonstrated.
Hardening md Tempering Steel.
Prof. Roberts-Austen, Of the Royal Mint,
concluded a recent lecture at Newcastle-on-
Tyne, England, by pointing to the impor-
tance of hardening and tempering in rela-
tion to all kinds OF steel. In the early days,
when steel was substituted for iron, it was
viewed with suspicion, mainly because the
fact that iron could exist in two distinct
molecular states was ignored. He showed
that the material of which the Forth bridge
is made owes its substantially to the fact
that. while being very strong, it is very so t
and ductile, and will not harden energetic
ally. The enormous Importance OF the sub
stitution of steel for iron was shown by fig
ures supplied by Mr.. Webb, of Crewe, who
stated that on the entire system Of the Lon
don and Northwestern Railway IS tons of
steel disappeared daily by oxidation and
wear. The Importance of oil hardening itf
relation to gun steel was shown by the fact
that at the st. Chamond Works, on the
Loire, they had tank containing A, 900
gallons of oil, into which the hot gun steel
was plunged. With regard to highly car
BOMBED steels, it was shown that properly
tempered die would strike 40, 900 coins, while
one which had beo over-hardened would
probably fracture with the first coin 1t at
tempted to strike. In conclusion Prot.
Austen said it was strange that so few re-
searches had been devoted to the relations of
carbon and iron and so many to organic
chemistry. This arose, he thought, from the
belief OF chemists and physicists that opera
tions which involved the use of high tenn
perature were necessarily inaccurate. He
considered, however, that the ''empire over
NATTER" which is the object Of all research,
could as surely be gained in the field of
metallurgy as in any other.