ignited, and tested in
a radiant matter tube gave as good a crimson line spectrum as did that
from the original sulphate.

A repetition of this purifying process gave no change in the result.
Four possible explanations are offered of the phenomena observed: "(1)
The crimson line is due to alumina, but it is capable of being
suppressed by an accompanying earth which concentrates toward one end
of the fractionations; (2) the crimson line is not due to alumina, but
is due to the presence of an accompanying earth concentrating toward
the other end of the fractionations; (3) the crimson line belongs to
alumina, but its full development requires certain precautions to be
observed in the time and intensity of ignition, degree of exhaustion,
or its absolute freedom from alkaline and other bodies carried down by
precipitated alumina and difficult to remove by washing; experience
not having yet shown which of these precautions are essential to the
full development of the crimson line and which are unessential; and
(4) the earth alumina is a compound molecule, one of its constituent
molecules giving the crimson line. According to this hypothesis,
alumina would be analogous to yttria."--_Nature._

* * * * *

CARBONIC ACID IN THE AIR.

By THOMAS C. VAN NUYS and BENJAMIN F. ADAMS, JR.

During the month of April, 1886, we made eighteen estimations of
carbonic acid in the air, employing Van Nuys' apparatus,[1] recently
described in this journal. These estimations were made in the
University Park, one-half mile from the town of Bloomington. The park
is hilly, thinly shaded, and higher than the surrounding country. The
formation is sub-carboniferous and altitude 228 meters. There are no
lowlands or swamps near. The estimations were made at 10 A.M.

[Footnote 1: See SCI. AM. SUPPLEMENT No. 577.]

The air was obtained one-half meter from the ground and about 100
meters from any of the university buildings. The number of volumes of
carbonic acid is calculated at zero C. and normal pressure 760 mm.

--------+----------+--------------+------------------------
| | Vols. CO_{2} |
Date. | Bar. | in 100,000 | State of Weather.
| Pressure | Vols. Air. |
--------+----------+--------------+------------------------
April 2 | 743.5 | 28.86 | Cloudy, snow on ground.
" 5 | 743.5 | 28.97 | " " " "
" 6 | 735 |