THE COMPOSITION OF WATER, HYDROGEN 149 



received that -i rater contains eight parts by weight of oxygen per one part 

 /ii/ /n !(//! f. of hydrogen. By whatever method water be obtained, it will 



anhydride, intermingled with lumps of pumice-stone. They are immersed in a freezing 

 mixture. The small U tube contains hygroscopic substances, and is weighed before the 

 experiment : this is in order to know whether the hydrogen passing through still retains 

 any moisture. If it does not, then the weight of this tube will not vary during the 

 whole experiment, but if the hydrogen evolved still retains moisture, the tube will in- 

 crease in weight. The copper oxide is dropped into the bulb, which is, previous to the 

 experiment, dried with the copper oxide during a long period of time. The air is 

 then exhausted from it, in order to weigh the oxide of copper in a vacuum and to 

 avoid making any correction for weighing in air. The bulb is made of infusible glass, 

 that it may be able to withstand a lengthy (20 hours) exposure to a red heat without 

 changing in form. The weighed bulb is only connected with the purifying apparatus after 

 the hydrogen has already passed through for a long time, and after experiment has shown 

 that the hydrogen passing from the purifying apparatus is pure and does not contain 

 any air. When the bulb is connected with the purifying apparatus, its cock is opened 

 and the hydrogen fills the bulb. The drawn-out end of the bulb is joined by an india- 

 rubber tube with the second bulb, in which the water formed is condensed. When this 

 connection is made, the thread binding up the india-rubber tube is untied, and then the 

 hydrogen can pass freely through the apparatus. On passing from the condensing bulb 

 the gas and vapour enter into an apparatus for absorbing the last traces of moisture. 

 The first U tube contains pieces of ignited potash, the second and third tubes phosphoric 

 anhydride or pumice-stone moistened with sulphuric acid. The last of the two is 

 employed for determining whether all the moisture is absorbed, and is therefore weighed 

 separately. The final tube only serves as a safety-tube for the whole apparatus, in order 

 that the external moisture should not penetrate into it. The glass cylinder contains 

 sulphuric acid, through which the excess of hydrogen passes; it enables the rate at 

 which the hydrogen is evolved to be judged, and whether its amount should be decreased 

 or increased. 



When the apparatus is set up it must be seen that all its parts are hermetically tight 

 before commencing the experiment. When the previously weighed parts are joined up 

 together and the whole apparatus put into communication, then the bulb containing the 

 copper oxide is heated with a spirit lamp (reduction does not take place without the aid 

 of heat), and the reduction of the copper oxide then takes place, and water is formed, 

 which condenses in the absorbing apparatus. When nearly all the copper oxide is re- 

 duced the lamp is removed and the apparatus allowed to cool, the current of hydrogen 

 being kept up all the time. When cool, the drawn-out end of the bulb is fused up, and 

 the hydrogen remaining in it is exhausted, in order that the copper may be again weighed in 

 a vacuum. The absorbing apparatus remains full of hydrogen, and would therefore present 

 a less weight than if it were full of air, as it was before the experiment, and, therefore, 

 having disconnected the copper oxide bulb, a current of dry air is passed through it until 

 the gas passing from the glass cylinder is quite free from hydrogen. The condensing 

 bulb and the two tubes next to it are then weighed, in order to determine the quantity of 

 water formed. Dumas repeated this experiment many times. The average result was 

 that water contains 1253'3 parts of hydrogen per 10000 parts of oxygen. Making a 

 correction for the amount of air contained in the sulphuric acid employed for producing 

 the hydrogen, Dumas obtained the average figure 1251'5, between the extremes 1247 -2 

 a n< I 1256-2. This proves that per 1 part of hydrogen water contains 7'9904 parts of 

 oxygen, with a possible error of not more than 7^, or 0'08, in the amount of oxygen per 

 1 part of hydrogen. 



Erdmann and Marchand, in eight determinations, found that per 10000 parts of 

 oxygen water contains an average of 1252 parts of hydrogen, with a difference of from 

 1258-5 to 1248-7 ; hence per 1 part of hydrogen there would be 7'9952 of oxygen, with an 

 error of at least 0'05, because, taking the figure 1258'5, the amount of oxygen per 1 

 part of hydrogen would be 7'944. 



