278 E W. Morley — Volumetric Composition of Water. 



tions that the part below the stopcock is shut off, and an open- 

 ing is left between the eudiometer and the outside of the 

 apparatus. By connecting the top of the eudiometer to an air 

 pump, aqua regia or potassium hydroxide can be drawn into 

 the eudiometer ; then by connecting the bottom of the eudi- 

 ometer to the pump, distilled water can be drawn in at the 

 top. In this way the tube was kept so clean that carbon 

 dioxide was formed only twice, when this washing was omit- 

 ted : accurate reading of volumes were also facilitated. Below 

 the glass stopcock, the eudiometer is connected by a rubber 

 connector, to a steel tube screwed into an iron stopcock. 

 The key of this stopcock is prolonged upwards some four 

 decimeters, and ends in the handle seen just above the reading 

 microscope. A small wheel imperfectly seen under the read- 

 ing microscope carries a series of stops of which any one can 

 be brought into position so as to arrest the opening of the 

 stopcock at a determinate point. This stopcock governs the 

 admission of mercury from the movable reservoir carried 

 vertically by an apparatus placed on a table to the left. The 

 iron stopcock has three steel tubes which are connected, one to 

 the eudiometer as said before, the others to the two pressure 

 tubes ; the smaller of these is an auxiliary, used for all rough 

 measurement, so as to reserve the other for the final accurate 

 measurement. This tube is shut off from connection with the 

 other tubes by a piston valve whose motion is produced by the 

 geared wheels seen at the left of the iron stopcock. Its 

 vacuum was easily kept unimpaired for months, as was proved 

 by repeated determinations. But further, this piston valve 

 also served as a micrometric adjustment of the level of the 

 mercury in the eudiometer and pressure tubes. The use made 

 of this will be mentioned below, and it contributed greatly to 

 the accuracy obtained. These three tubes were enclosed in a 

 box with glass front and back, and filled with clear water kept 

 stirred by a current of air. The eudiometer is secured into a 

 brass plate which is ground water-tight to the bottom of the 

 box : on removing a clamp, the eudiometer can be lifted out 

 of place if necessary, and can be replaced without a variation 

 of its level amounting to the hundredth of a millimeter. It 

 was convenient to compute the measured volumes of gases by 

 means of an interpolation formula whose constants depended 

 on the relative levels of fiducial marks on the eudiometer and 

 pressure tubes, and constancy of this relation even after re- 

 moving the eudiometer, was highly desirable. The pressure 

 tube was provided with a fine screw motion by which it could 

 be adjusted vertically while in position and filled ready for 



use. 



The recurved tube at the upper end of the eudiometer 

 serves for the introduction of gas into the apparatus. The 



