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.

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.

Date.Bar. PressureVols. CO2
in 100,000
Vols. Air.
State of Weather.
April2743.528.86Cloudy, snow on ground.
"7744.528.63Clear, snow on ground.
"874827.59Clear, thawing.

The average number of volumes of carbonic acid in 100,000 volumes of air is 28.16, the maximum number is 28.98, and the minimum 27.34. These results agree with estimations made within the last ten or fifteen years. Reiset2 made a great number of estimations from September 9, 1872, to August 20, 1873, the average of which is 29.42. Six years later3 he made many estimations from June to November, the average of which is 29.78. The average of Schultze's4 estimations is 29 2. The results of estimations of carbonic acid in the air, made under the supervision of Munz and Aubin5 in October, November, and December, 1882, at the stations where observations were made of the transit of Venus by astronomers sent out by the French government, yield the average, for all stations north of the equator to latitude 29° 54' in Florida, 28.2 volumes carbonic acid in 100,000 volumes air, and for all stations south of the equator 27.1 volumes. The average of Claesson's6 estimations is 27.9 volumes, his maximum number is 32.7, and his minimum is 23.7. It is apparent, from the results of estimations of carbonic acid of the air of various parts of the globe, by the employment of apparatus with which errors are avoided, that the quantity of carbonic acid is subject to slight variation, and not, as stated in nearly all text books of science, from 4 to 6 volumes in 10,000 volumes of air; and it is further apparent that the law of Schloesing7 holds good.

By this law the carbonic acid of an atmosphere in contact with water containing calcium or magnesium carbonate in solution is dissolved according to the tension of the carbonic acid; that is, by an increased quantity its tension increases, and more would pass in solution in the form of bicarbonates. On the other hand, by diminishing the quantity of carbonic acid in the atmosphere, some of the bicarbonates would decompose and carbonic acid pass into the atmosphere.

Schloesing's law has been verified by R. Engel8.

The results of estimations of bases and carbonic acid in the water of the English Channel lead Schloesing9 to conclude that the carbonic acid combined with normal carbonates, forming bicarbonates, dissolved in the water of the globe is ten times greater in quantity than that of the atmosphere, and on account of this available carbonic acid, if the atmosphere should be deprived of some of its carbonic acid, the loss would soon be supplied.

As, in nearly all of the methods which were employed for estimating carbonic acid in the air, provision is not made for the exclusion of air not measured containing carbonic acid from the alkaline fluid before titrating or weighing, the results are generally too high and show a far greater variation than is found by more exact methods. For example, Gilm10 found from 36 to 48 volumes; Levy's11 average is 34 volumes; De Luna's12 50 volumes; and Fodor's,13 38.9 volumes. Admitting that the quantity of carbonic acid in the air is subject to variation, yet the results of Reiset's and Schultze's estimations go to prove that the variation is within narrow limits.

Indiana University Chemical Laboratory,
Bloomington, Indiana.

- Amer. Chem. Journal.


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