a specimen of alumina prepared from tolerably pure aluminum sulphate, shown by the ordinary tests to be free from chromium, the bright crimson line, to which the red phosphorescent light is due, was brightly visible in its spectrum. The aluminum sulphate was then, in separate portions, purified by various processes especially adapted to separate from it any chromium that might be present; the best of these being that given by Wohler, solution in excess of potassium hydrate and precipitation of the alumina by a current of chlorine. The alumina filtered off, 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.

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.

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 Schloesing