22.-HYDROGEN BY NEW METHOD. VERIFICATION OF ACCURACY OF WEIGHTS. The accuracy of the weights used for determining the weights of hydrogen received careful attention. I determined the relation of each weight of two additional sets of small weights to the kilogramme of the set marked K, on which all my determinations of volume depend. Then determinations of weights of hydrogen were made with all these four sets of weights; so that it is improbable that any serious error is due to the uncertainty of the values of the weights employed. I moreover determined the relation to the same kilogramme of two other sets of small weights which were kept simply for the purpose of comparing them with the weights which were used in weighings, so as to detect any accident to any of these. 23.-HYDROGEN BY NEW METHOD. REDUCTION OF OBSERVATIONS. The readings of the barometer were corrected by means of the table given by Landolt and Boernstein. The corrected numbers are called observed values. To the capacities of the globes at 0° was added the capacity of that part of the connecting tubes which was always covered with ice. The volume contained by the syphon barometer down to the mark noted was taken from the table on page 68, and reduced to the volume which that amount of gas would have at 0°. The three or four cubic centimetres which were not below the water level of the case surrounding the barometer were assumed to be at the temperature of the barometer; which was near enough to the truth. The sum of these three volumes made up the observed volume. The observed temperature is that of melting ice; the elevation of the cistern of the barometer introduces a correction of less than five thousandths of a millimetre of mercury. We have therefore The table gives the observations of the third and fourth series, together with some observations which were unsuccessful on account of various slight accidents or unforeseen circumstances. Five columns define the volumes which are to be added to the calibrated capacities of the globes; these show the mark at which the mercury stood in the barometer, the temperature here, the volume corresponding this volume reduced to 0°, and the volume of the tubes which were covered with ice. Next is shown the volume of the globes, the total volume, the pressure reduced to 0°, but uncorrected for the length of my bar, the observed weight of hydrogen, and the density computed for the sea level in latitude 45°. 42.1111 I Oct'r 19 282.7 21.6 2 3 25 4 31 5 Nov'r 2 6 43.9 40.7 41.6 42.IIII 42.1934 704.43 3.5171 [.089972] 42.2027 742.83 3.7057 .089877 42.2016 740.66 3.6944 .089867 42.2016 740.84 3.6973 .089916 42 2007 738.33 3.6790 1.089777] 42.IIII 42.2046 743.51 3.7080 .089846 If we increase the means by one thirty-thousandth,* we have = Series III., Dh 25.--HYDROGEN BY NEW METHOD. 0.000004 9 SOURCES OF ERROR. If, after measuring the vacuum in the globes, leakage occurred, the pressure of the hydrogen in the manometer would appear too great, and the density, therefore, too small. Now it is believed that in experiment 5 of series iv. this accident occurred. The key of stopcock e, Fig. 23, was found, afterwards, to have formed an incipient crack at some previous and unknown time, and leakage from this cause had become so troublesome that, unable to detect the real source, and ascribing it to the wrong source, I broke up the apparatus and made a new one in which leakage was impossible, and in which it never took place. This crack was in such a position on the key that the leak was likely to be developed only when the stopcock * See note, page 28. Density of hydrogen: grammes. was closed, and only when, in closing, the crack was turned towards the globes. This determination ought fairly to be rejected, although there was no means of knowing, at the time, that leakage was actually taking place. There were some accidents which might make the weight of a litre of hydrogen appear too high. In breaking off the point k, Fig. 25, an unnoticed fragment might be lost. The asbestos in h, if not properly adjusted, might permit the escape of a globule of the melted metal. If the moisture absorbed by the asbestos during the construction of the tube was not removed during the first exhaustion of the space gk, Fig. 25, it would be given off with the hydrogen. Either of these would make the weight of the hydrogen expelled from the tube appear too great. It was thought that the first experiment of series iv. was in error from the first of these causes, though the evidence was not so conclusive as to lead to the instant abandonment of the experiment. Five experiments were made before the proper conduct of the experiment was mastered. The mishaps were various, and perhaps do not need to be detailed. The observations are given, though they are not used in obtaining the final mean. 26. HYDROGEN BY NEW METHOD. SECOND APPARATUS. The determinations of series iii. were made as soon as the apparatus was put together and the preliminary experiments finished, and while the apparatus was in perfect order. The stopcocks showed no leakage even in a somewhat protracted test. But after an absence during the summer, much trouble was experienced, of which the true cause was not easily learned. Leakage appeared, sometimes slow, but sometimes rapid or capricious, so that many experiments were abandoned at different stages. Fresh lubrication of the stopcocks not helping much, they were surrounded with rubber capsules holding glycerine. This stopped the leakage long enough to get the results of series iv., but the leakage then became so capricious that sometimes an action of the pump which ought to have given a vacuum of one millionth left one or two thousandths instead. The apparatus was broken up and replaced with one which should be proof against leakage; some time afterwards the nature of the difficulty was learned. The crack in the key of the stopcock caused the small leak. The rubber capsules holding glycerine, by continued pressure, gradually loosened the key of one stopcock, admitting glycerine, then water, and finally air; hence the larger and capricious leakage. 27.-HYDROGEN BY NEW METHOD. SECOND APPARATUS. CAPACITY OF GLOBES. It will have been noticed that the stopcocks of the three globes, Fig. 23, were useful only during the measurement of the capacity of the connecting tubes. The stopcocks leading to the pump could be easily replaced by a U-shaped tube filled with mercury when the passage was to be interrupted, and the stopcocks of the globes could be replaced with plugs of fusible metal. Three globes were therefore arranged as shown in Fig. 28. At m, n, were plugs of fusible metal closing the tubes which connect the globes to the other apparatus. Each globe was weighed in air and then in water before these tubes were applied, and before the necks of the globes were drawn out; from which could be computed the solid contents of the globe, or rather the specific gravity of the glass of that globe. The globes were then brought to the form shown in the figure, but with the horizontal tube only a few centimetres long, and were again weighed in air and in water so as to determine their external volume, just as in case of the globes used for oxygen. The weighing being repeated at a different temperature the capacities of the globes were thought to be sufficiently well determined. The table gives the data of the experiments together with the capacities inferred. Weights are corrected for air displaced by objects weighed and by weights used; temperatures are made to correspond with the true scale of a thermometer of mercury in Jena normal glass. From the foregoing determinations of the external volume and solid contents of each globe, we get the capacities as follows: This is the value to be used for the experiments (on another matter) after January 18th. But during the experiments of this series, there were 18 grammes of mercury in globe A, introduced by slight accident. The volume to be subtracted from the capacity of the globes is therefore 1.3 cubic centimetres, and the effective capacity during the experiments of this series was therefore 43257.4 cubic centimetres. 28.-HYDROGEN BY NEW METHOD. SECOND APPARATUS. CONNECTION OF GLOBES TO PUMP AND BAROMETER. The globes called A, B, and C were now placed in the cylinders which were to protect them from the contact of large fragments of ice, and were packed in finely crushed ice, and connected as shown in Fig. 28. The tube c led to the FIG. 28.-Second apparatus for receiving hydrogen and measuring its volume and pressure at constant temperature : globes without stopcocks. upper edge of the tank where it joined the mercurial valve shown at fy h, which was interposed between the globes and the pump. At i was a mark. In measurements of the pressure of hydrogen in the globes, the level of the mercury in the mercurial valve was always brought to this mark. All the tubes between this |