July i6, 1896] 



NA TURE 



259 



and filled with water. A small tube led from the cylinder to a 

 burette containing water. When the globe was exhausted the 

 compression was measured by the amount of water run into the 

 cylinder from the burette. Each globe was provided with a 

 counterpoise of equal external volume when exhausted. A pair 

 of small flasks were then made, the difference between whose 

 volumes was equal to the amount of compression just measured, 

 and whose weights in vacuo were equal. 



For example, the actual compression of one globe was I "27 cc. 

 The two small flasks were made 2'oS and 'Si cc. in volume 

 and of the same weight when weighed in vacuo ; therefore when 

 weighed in air they differed in weight by the weight of i '27 cc. 

 of the air at the time, taking into account the true value of the 

 weights employed. When the globe was exhausted it was 

 weighed against the counterpoise which had the same volume. 

 When it wa.s full of gas it was tared with the "81 cc. flask 

 against the counterpoise and the 2'oScc. flask ; \.\\^true weights 

 of the globes therefore suffered equal additions, with the result 

 that tlie apparent difference in weight would be the true difference 

 as expressed by brass weights in air. 



The measurement of pressure and temperature. Dr. Morley 

 took especial pains to make as accurate as possible. In the 

 many series of experiments which are comprised in this great 

 research, different methods were adopted of measuring these 

 values. When thermometers were used great care was taken in 

 determining their errors, and in the calculation of the pressures 

 the value of the force of gravity as actually determined at Dr. 

 Morley's laboratory was used. 



Dr. Morley's determinations are divided into four series. 



The first series consists of the determination of the weight 

 of one litre of oxygen. 



The second series consists of a similar determination for 

 hydrogen. 



The third series contains some experiments to determine the 

 volumetric composition of water. 



The fourth is a series of syntheses of weighed quantities of 

 water from weighed quantities of oxygen and hydrogen. 



The first series of determinations are those of the weight of a 

 litre of oxygen under standard conditions. Three different 

 methods were adopted. 



In the first the temperature and pressure were directly deter- 

 mined by use of thermometers and a manobarometer. 



In the second method the temperature and pressure were not 

 directly determined, but made equal to those of a standard 

 volume of hydrogen. 



In the third method the pressure was alone read, the tempera- 

 ture being that of melting ice. 



The oxygen for this series of experiments was obtained from 

 potassium chlorate. The salt was placed in a hard glass tube in a 

 .comliustion furnace ; this tube was joined to the rest of the 

 apparatus by means of a ground joint cemented with wax. Dr. 

 Morley made a point of using no rubber connections in any of his 

 experiments, rightly observing that even though the leakage may 

 be exceedingly small, still the extra trouble entailed by fusing all 

 joints together is worthily bestowed. Dr. Morley says there is 

 no reason to doubt the purity of this oxygen ; nitrogen he sought 

 for ])articularly, and found quantities varying from 1/12, 000th 

 to I 5,000,000th, which are quite negligible, considering the 

 closeness of the atomic weights of the two gases. 



Dr. Morley discusses the question of mercury vapour, and 

 reasons from his experiments on hydrogen that the error is not 

 greater than the ten- or twenty-thousandth part of the density of 

 oxygen. 



The pressure in these experiments was measured by means of 

 a manobarometer, which consisted of a barometer and two 

 gauges mounted in the same trough of mercury. One of these 

 gauges was used for oxygen and the other for hydrogen, the ex- 

 periments on which were carried out at the same time. The 

 liarometer and gauges were placed in a cistern of water with 

 plale-glass sides. In front of each tube, and in contact with it, 

 was a glass millimetre scale. The three scales were adjusted so 

 that their zero points were all on the same level. The calheto- 

 meter used for reading had two telescojies, each with a micro- 

 meter eyepiece. The accuracy of reading was found to be 

 within I 1 00th mm. 



In weighing the globes Dr. Morley met at first with great 

 difficulty, owing to currents of air disturbing the globes. Their 

 effect was, however, almost destroyed Ijy hanging the globes in 

 a sheet-iron box, which was in its turn placed in a non-con- 

 ducting chamber under the balance. The balance was one 



ND. 1394, VOL. 54] 



of Becker's make, and had never been used for any other 

 purpose. 



The mean of nine determinations by this method of the weight 

 of a litre of oxygen is 



I '42879 gr. ± -000034. 



In the second method of weighing oxygen, the pressure and 

 temperature were made equal to those of a standard volume of 

 hydrogen. The preliminary part of this process was to fill a globe 

 with pure hydrogen, and measure the pressure exerted by the gas 

 on one leg of a differential manometer. This instrument was 

 of the ordinary U shape, adjustment of the mercury being made 

 to two needle-points, one in each limb. The globe containing 

 the oxygen was then attached to the opposite limb, and the 

 pressure adjusted till exactly equal to that of the hydrogen. A 

 new balance was employed in these determinations, purchased 

 especially for this work, and lent Dr. Morley by the Smithsonian 

 Institution. Weighing was performed by reversal, the relative 

 position of globe and counterpoise being changed by mechanical 

 means. 



Dr. Morley publishes fifteen determinations of the weight of a 

 litre of oxygen by this method. The mean is 



I '42887 gr. + '000048. 

 The method employed in the third series of determinations 

 was to determine the pressure of the oxygen by means of the 

 syphon barometer, the temperature being 0° C. The globe was 

 immersed in ice, the layer of ice all round the globe being 30 

 centimetres thick. The globe was then exhausted and oxygen 

 admitted, and its pressure measured. After weighing the globe 

 was again exhausted and again weighed, the difference being 

 taken as the weight of the oxygen. The reason for this procedure 

 was the fact of the globe being exposed to the action of water 

 for such a long time. 



As a mean of twenty-four experiments, Dr. Morley gives 



D = I '4291 7 gr. ± '000048. 

 We have, therefore, the following three mean results by the 

 three different methods. 



By use of thermometer and mano- 

 barometer ... ... ... I '42879 + '000034 



By compensation ... ... ... i '42887 '000048 



By use of ice and barometer ... i '42917 '000048 



In computing a final mean from these, Dr. Morley discusses 

 the relative reliability of the results. He gives double weight to 

 the third method, for, though involving more accidental errors, it 

 involves no constant error common to the other methods. 



Dr. Morley gives his final value for the weight of i litre of 

 oxygen measured at 0° and 760 mm. at sea-level, and 45° lat., as 

 I '42900 gr. + '000034. 



The second part of Dr. Morley's paper deals with his deter- 

 minations of the weight of i litre of hydrogen under standard 

 conditions. 



Five series were made. In the first, pressure and temperature 

 were measured ; in the second, pressure. only was measured, the 

 temperature being equal to that of melting ice ; in the third, 

 the hydrogen was weighed in combination with palladium before 

 introduction into the globe. The fourth and fifth were repeti- 

 tions of the third. 



The first series of determinations were carried out in exactly the 

 same manner as the first series with oxygen, indeed at the same 

 time. The hydrogen was prepared by the electrolysis of dilute 

 sulphuric acid. 



Dr. Morley adopted elaborate methods to measure the 

 impurity in the hydrogen. He introduced a correction foi; the 

 nitrogen found until, owing to an improvement of the apparatus, 

 this percentage of nitrogen became so small as to be entirely 

 negligible. 



The mean of fifteen results obtained by this method is 



D = '089938 gr. + '000007. 



The second method was to read pressure only, the temperature 

 being 0° C. The details are exactly the same as in the similar 

 case with oxygen. 



The mean of nineteen experiments is 



D = '089970 + 'ooooii. 



The third method, that of weighing the hydrogen contained in 

 palladium, is one that is far more likely to prove accurate than 

 methods depending on the weighing directly of a known volume 



