Lederberg, Esther M. to Cavalli-Sforza, Luca Luigi
June 13, 1965
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To ease reading, a transcription of the first paragraph (above) follows.
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If velveteen of acceptable quality that had not been
waterproofed ("scotch-guarded") was unavailable, filter paper
could be used temporarily to simultate replica plating.
However, just as there were different levels of quality
to velveteen, there were also different levels of quality
in filter paper. These kinds of problems with filter paper
were well-known to chemists who had studied inorganic
quantitative analysis.
Inorganic quantitative analysis has three major branches
of study:
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Titrimetric analysis (soultions of standardized strength
using various "indicators", electro-chemical methods,
use of radioactive chemicals)
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Gravimetric analysis.
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Special Instrumentation (such as chromatography)
Gravimetric analysis consists of collecting a precipitate
from solution using filter paper, then measuring the
quantity of precipitate. To measure the quantity of
precipitate, the precipitate in the filter paper is
thoroughly dessicated, then slowly burned in
accurately pre-weighed numbered crucibles with numbered
covers. If the exact weights of the crucibles, covers,
and the ash-weight of the
filters is subtracted from the total weight, the remaining
weight is the weight of the precipitate. For gravimetric
analysis to provide accurate weights, several factors are
important, such as there being no reaction of the precipitate
with the environment; and most crucially, a precise knowledge
of the exact ash-weight of the
filter paper. The quality of the filter paper is analogous to
the quality of the velveteen used in replica plating. For
example, heavy metals in filter paper could act as a poison
to bacteria or interfere with measurements being assayed in
an experiment.
It was well known that replica plating was superior to other
similar methods such as using filter paper, prongs, etc, but
virtually all researchers recognized that replica plating
was the best method to replicate many colonies at one time.
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