LIST OF ILLUSTRATIONS. FIGURE 1.--Preliminary Weighing of a Globe. 2.- Hydrostatic Weighing of Small Globes 3.-Collar and Pan for Submersion of Globes 4.-Apparatus for Measuring Compression of Globes on Exhaustion. PAGE 3 7 8 14 5.-Discharge Tube of Toepler Pump for Obtaining a Better Vacuum 17 6. Calorimeter Case for Measuring Temperature of Oxygen 19 7.-Apparatus for Preparing Oxygen. 8. Barometer and Reading Microscopes Pointer 20 23 9.-Balance Surrounded with Non-Conducting Case; Illumination of Scale and 10.-Balance, Case, and Metal Box, for Accurate Weighing of Globe. II.-Globe Containing Hydrogen for a Standard of Comparison. 12.-Mounting of Differential Manometer to Maintain its Position Undisturbed 15.-Filling Globe with Oxygen; Use of Desiccator; Hydrogen Used for Comparison, 16.—Balance Standing on the Closet which Contains the Mechanism for Transferring Objects from One Pan of the Balance to the Other. 37 38 17.-One Arm of Revolving Carrier, Raised, Hooks Disengaged 18.—One Arm of Revolving Carrier, Lowered, Hooks Engaged 39 40 19.-Plan of Reversing Mechanism 41 20.—Method of Preventing Leakage of Globes when Exhausted. 47 21.-Small Flask for Equalizing Volumes 48 24.--Apparatus for Determining Volume of Connecting Tubes. 22.-Filling a Globe with Oxygen; Use of Ice 22 a. Desiccator . 23.-Apparatus for Receiving Hydrogen and Measuring its Volume and Pressure at Constant Temperature 52 54 66 67 25.-Palladium Tube with no Stopcock 70 26.-Palladium Tube, Ready to Connect to Apparatus 71 27.-Palladium Tube, Connected to Apparatus, Connection Exhausted 71 28.-Second Apparatus for Receiving Hydrogen and Measuring its Volume and 29.--Method of Connecting Voltameter and Regulating the Current 31.-Voltameter for Producing and Weighing Mixed Gases. 85 32.-Toepler Pump Used to Measure Sample for Analysis; Small Toepler Pump for Transferring Convenient Quantity to Eudiometer 88 33.-Palladium Tube, First Form. 97 34.-Palladium Tube, Protected against Leakage through Stopcock 98 38.-Manipulator, Rear View, with Globes and Palladium Tube Connected 102 39.-Apparatus for Detecting Absorption of Oxygen by Phosphorus Pentoxide; Filling with Oxygen 40.-Apparatus for Detecting Absorption of Oxygen by Phosphorus Pentoxide; Set up for the Experiment 107 108 ON THE DENSITIES OF OXYGEN AND HYDROGEN, AND ON THE RATIO OF THEIR ATOMIC Weights. BY EDWARD W. MORLEY. PART I-ON THE DENSITY OF OXYGEN. 1. INTRODUCTION. The first part of this paper describes three series of determinations of the density of oxygen. In the first series, the pressure and temperature of the gas to be weighed were determined with mercurial thermometers and a manobarometer. In the second series, pressure and temperature were not determined for each experiment, but were made equal to the pressure and temperature of a standard volume of hydrogen, the comparison being made by means of a differential manometer. In the third series, the temperature was that of melting ice, so that the mano-barometer alone was observed. In the first series, the surfaces of the globes in which the oxygen was weighed were hardly touched during the manipulation; and not touched at all in the second series. In the third series, the globes were in contact with cold water for a considerable time. The stopcocks were covered with rubber capsules during this exposure, but it seems that this protection did not much lessen the uncertainty usually noticed in the weight of glass so exposed. In the reduction of each observation of the first series, account was taken of : 1. The expansion of the glass of the globes; 2. The errors of the two mercurial thermometers; 3. The deviation of the mercurial thermometer from the hydrogen airthermometer; 4. The difference between the coefficients of expansion of hydrogen and of oxygen; 5. The elevation of the cistern of the mano-barometer above the centre of the globe while the latter was filling with oxygen; 6. The correction to the length of the scale of my mano-barometer; and 7. The force of gravity at my laboratory. In the second series, the first three of these seven factors were eliminated, for thermometers were not used, and the expansion of the globe in which the oxygen had its pressure measured was compensated by the equal expansion of the similar globe containing the standard volume of hydrogen. In the third series, the cistern of the mano-barometer, which was then used as a syphon barometer, was at the level of the centre of the globe, so that the observations were reduced by taking account simply of the length of my scale and of the force of gravity at my laboratory. In the forty-one determinations which are included in the three series, eight different globes were used, in order to eliminate the effect of accidental errors in the determinations of their capacity. 2.-MEASUREMENT OF CAPACITIES OF GLOBES. My measurements of the capacities of the globes used for weighing oxygen involved three processes, as follows: 1. The determination of the weight of the globe in air; 2. The determination of the weight required to be added to maintain the globe in equilibrium when immersed in water of known temperature; and 3. The determination of the loss of weight of the globe when full of water and immersed in water of the same temperature. Combining the first determination with the second, we get the external volume of the globe; from the third and first determinations we get the solid contents of the material of which the globe is composed. The difference between the external volume and the solid contents gives the capacity. It is obvious that a determination of the weight of the water required to fill the globe at a known temperature would form a more direct and a more accurate determination of its capacity; but this would have required the use of a balance carrying twenty-five kilogrammes in each pan, which I should have had to purchase for the purpose. As the other expenses of the investigation were a heavy burden, the method just described was used; it is hoped that the results of the determinations will be found to have been sufficiently accurate. As the errors of the calibrations seem to have been made much less than the accidental errors of single experiments, as the number of calibrations of each globe was not too small, and as so many globes were calibrated and used in the determination of density, no error of sensible magnitude is likely to have been caused. |