1889.] On the Composition of Water. 427 



From the quantity of that gas which proved to be in excess, the cal- 

 culated weight of the residue is subtracted. This gives the weight of 

 the two gases which actually took part in the combustion. 



In practice, the operation is more difficult than might be supposed 

 from the above description. The efficient capacity of the eudiometer 

 being necessarily somewhat limited, the gases must be fed in through- 

 out in very nearly the equivalent proportions ; otherwise there would 

 soon be such an accumulation of residue that no further progress 

 could be made. For this reason nothing could be done until the 

 intermediate mixing chamber was provided. In starting a com- 

 bustion, this vessel, originally full of mercury, was charged with 

 equivalent quantities of the two gases. The oxygen was first admitted 

 until the level of the mercury had dropped to a certain mark, and 

 subsequently the hydrogen down to a second mark, whose position 

 relatively to the first was determined by preliminary measurements 

 of volume. The mixed gases might then be drawn off into the 

 eudiometer until exhausted, after which the chamber might be re- 

 charged as before. But a good deal of time may be saved by 

 replenishing the chamber from the globes simultaneously with the 

 exhaustion into the eudiometer. In order to do this without losing 

 the proper proportion, simple mercury manometers were provided for 

 indicating the pressures of the gases at any time remaining in the 

 globes. But even with this assistance close attention was necessary 

 to obviate an accumulation of residual gas in the eudiometer, such as 

 would endanger the success of the experiment, or, at least, entail 

 tedious delay. To obtain a reasonable control, two sparking places 

 were provided, of which the upper was situate nearly at the top of 

 the eudiometer. This was employed at the close, and whenever in 

 the course of the combustion the residual gas chanced to be much 

 reduced in quantity ; but, as a rule, the explosions were made from 

 the lower sparking point. The most convenient state of things was 

 attained when the tube contained excess of oxygen down to a point 

 somewhat below the lower sparking wires. Under these circum- 

 stances, each bubble of explosive gas readily found its way to the 

 sparks, and there was no tendency to a dangerous accumulation of 

 mixed gas before an explosion took place. When the gas in excess 

 was hydrogen, the manipulation was more difficult, on account of the 

 greater density of the explosive gas retarding its travel to the 

 necessary height. 



In spite of all precautions several attempted determinations have 

 failed from various causes, such as fracture of the eudiometer and 

 others which it is not necessary here to particularise, leading to the 

 loss of much labour. Five results only can at present be reported, 

 and are as follows : 



