Chemistry and Physics. 49 



between the objective and the reflecting mirror A or else 

 mounted on the mirror frame itself so as to rotate with it. The 

 last position enables the same instrument to be used either in 

 the method of comparison or in the method of coincidence, but 

 it is objectionable both on account of the increased weight of 

 the moving parts and because of the liability of disturbing the 

 adjustment of the axis or mirror while manipulating the 

 micrometer. It is therefore better to place the rotating plate 

 in the first position indicated and adapt it to either method of 

 use if desired, by making it cover only one-half the field of the 

 telescope, that half of course which is opposite the unsilvered 

 half of the mirror when the coincidence method is used, and 

 opposite the silvered half when the comparison method is 

 employed. 



In closing I wish to express my thanks to Messrs. Francis 

 and Kathan, the mechanicians of the laboratory, for the care 

 exercised in the mechanical execution of these designs. 



University of Chicago, September, 1895. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistey and Physics. 



1. The Determination of Argon. — By the use of an elaborate 

 apparatus, Schlohsing Jr. has carefully determined the amount 

 of argon in the air. The arrangement was such that the atmo- 

 spheric " nitrogen " was gradually supplied to the apparatus 

 where it circulated over heated magnesium and copper oxide and 

 through drying apparatus, and the last traces of nitrogen were 

 finally removed by sparking with oxygen. The method was 

 tested by mixing the purest obtainable argon with chemical nitro- 

 gen in the same proportion in which they exist in the air and 

 subjecting the mixture to analysis. These tests gave excellent 

 results but showed a slight loss of argon. The author concludes 

 that 100 volumes of atmospheric nitrogen and argon contain 

 1*183 volumes of argon, while air as a whole contains 0'935 per 

 cent by volume. He believes that these numbers are correct 

 within -j-J-g- of their value. — Compt. IZend., cxxi, 525. 



In a subsequent article the above-mentioned author describes a 

 continuation of his experiments. Repeated tests of the method 

 invariably showed a loss of argon amounting, on the average, to 

 about 0*7 per cent. This loss is not satisfactorily explained, but 

 the possibility is suggested that argon may have some slight 

 action upon hot metallic magnesium. The author gives the 

 results of a number of analyses, as follows : 



Am. Jour. Scl— Fourth Series, Vol. I, No. 1.— January, 1896. 

 4 



