288 F TT. Mar — Estimation of Barium as the Sulphate. 



less than the hundredth of a cubic centimeter of nitrogen in 

 two liters of hydrogen, and containing no other impurity in 

 amount large enough to be detected. By the use of a fusible 

 metal valve, it was possible to obtain any required degree of 

 exhaustion in the part of the apparatus designed to receive 

 hydrogen from the generator. The hydrogen intended to be 

 weighed was not suffered to take up mercurial vapor, nor that 

 intended for analysis to be contaminated with organic matter. 

 A supply of hydrogen sufficient for several experiments was so 

 stored up as to be safe from admixture of air ; so that by the 

 apparatus described, the amount of nitrogen in it could be 

 determined in duplicate, and other quantities identical in 

 composition could be used for determining simultaneously 

 the amount of nitrogen in the oxygen used, and also the 

 volumetric composition of water. An apparatus for the mea- 

 surement of gases has been constructed in which the mean 

 error of measurement of the volume of hydrogen and oxygen 

 used in the experiments has been less than one part in fifty 

 thousand. With this, twenty experiments have been made 

 (four others being lost by accident and not completed), which 

 gave a maximum value for the composition of water 2"0u047, a 

 minimum value 2*00005, and a mean value 2"00023. Varia- 

 tions in the process gave no corresponding variation in the 

 result. The mean error of a single determination was one part 

 in twenty-six thousand. 



For the present, then, we may believe that water, when the 

 gases are measured under ordinary temperatures and pressures, 

 is composed of 2 -0002 volumes of hydrogen to one volume of 

 oxygen ; or that under ordinary conditions, the number of mole- 

 cules in a given volume of oxygen is one nine thousandth part 

 greater than the number of molecules in an equal volume of 

 hydrogen. 



Art. XXXII. — On certain points in the Estimation of Ba- 

 rium as the Sulphate ; by F. W. Mar. 



[Contributions from the Kent Chemical Laboratory of Tale College. — VI.] 



In the received mode of precipitating barium as barium 

 sulphate, three conditions are carefully observed — absence of 

 excess of acid, slow mixing of the reagents and rest, before 

 filtration, of twelve hours or until the precipitate has com- 

 pletely subsided. Usually, in this process, the precipitate is 

 thrown out in a finely divided, milky condition and settles 

 very slowly. My observation that the precipitate, under cer- 

 tain circumstances, is formed in a more crystalline condition 



