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OCR Page 1 of 5copy
DEPARTMENT OF COMMERCE
Bureau of Standards,
Washington, D.C.
July 16th, 1918.
Radium Luminous Material Corp'n
55 Liberty Street,
New York City.
Gentlemen:-
In accordance with your request of May 23rd
the study of the 12 cards of illuminated figures and dots
covered by our tést No. 23319 and our report of May 14
has been continued. Summaries of the results obtained
will be found in tables I,II, and III, enclosed herewith.
In our letter of May 28th attention was
called to the effect of humidity upon the brightness.
This phenomenon has been studied. The results obtained
indicate, not only that an exposure to high humidity reduces
the brightness, but also that the reduction takes place rather
radpidly, and the brightness becomes fairly constant after a
day or two. On the other hand the reverse change in drying
may be quite slow; when a card that has been kept in a
humidor for several days is transferred to a dessicator,
several days may elapse before a marked increase in brightness
is observed. An illustration of the variations observed is
given in Table I. It will be observed that figures on the
same card do not all behave alike.
The values observed after drying the cards over
calcium chloride are given in Table II. It will be noted
that A and F had not been in the dessicator so long as the
other cards. Those two cards had been kept in a humidor in
a nearly saturated atmosphere for several days before they
were placed in the dessicator. The other cards have at no
time been placed in the humidor.
A better insight into the relative behavior
of the luminous material upon the different cards will be
obtained by studying groups instead of individual markings.
The grouping will eliminate to some extent both the
experimental errors and the idiosyncrasies of the individual
marks. In Table III the observations have been grouped as
follows:
Group "I to 5" includes the 5 smallest figures,
group "10 to 14", the 5 largest figures, and group "6 to 9"
the 4 dots. In the table are given the average brightness of
each group as observed on each of 3 days, and also the
relative brightness of each group in terms of its brightness at
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