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     |    28.61     | Snowing.
"   7 |  744.5   |    28.63     | Clear, snow on ground.
"   8 |  748     |    27.59     |   "    thawing.
"   9 |  747.5   |    28.10     |   "       "
"  12 |  744     |    28.04     | Cloudy.
"  13 |  744     |    28.10     | Clear.
"  14 |  743.5   |    28.98     |   "
"  15 |  750.5   |    28.17     | Raining.
"  19 |  748     |    28.09     | Clear.
"  20 |  746     |    27.72     |   "
"  21 |  746     |    28.16     |   "
"  22 |  741.5   |    27.92     |   "
"  23 |  740     |    28.12     |   "