OF THE PARAFFINS AND THEIR MONOHALOGEN DERIVATIVES. 
15 
There must be no water left in the apparatus, or in spite of chemical equations 
some free hydrogen will be given off. The couple was several times washed with 
alcohol, which had been scrupulously dried with lime and anhydrous copper sulphate. 
The copper-zinc couple itself seemed to be the best drying agent for removing the 
last traces of water, for the apparatus gave purer methane the second or third time 
of using than it did the first time ; hence, after setting it up it is advisable to put in a 
little methyl iodide, and allow it to stand for a day or two with a Bunsen valve or 
some such arrangement attached. 
The gas that comes over first is purest, so that no attempt should be made to 
secure a theoretical yield. 
A considerable quantity of methyl iodide escapes the scrubber, and must be 
removed in some way. A set of Geissler bulbs filled with fuming sulphuric acid was 
used in this and similar cases and proved quite effective. The first bulb blackened 
and deposited iodine long before the second was coloured, and many litres of gas 
could be passed through before the colour reached the third bulb. This introduced 
sulphur dioxide into the gas, to remove which it was collected in a gas-holder over 
soda solution and shaken with it. 
It was admitted into the Kundt apparatus through three U-tubes, the first 
containing solid potash, to remove any sulphur dioxide still remaining, the second 
containing nine grams of palladium black as a precaution to retain any free hydrogen, 
and the third containing pumice soaked in sulphuric acid to dry the gas. 
Palladium is not altogether satisfactory for the removal of hydrogen ; it is very fickle 
in its action, sometimes for no obvious reason refusing to absorb it. In the preliminary 
experiments and in the preparation of propane, to be described later, 30 grams of thin 
foil, superficially oxidized by ignition in air, was used, but this, though quite effective 
in removing the greater part of the hydrogen, which was all that was wanted in the 
case of propane, failed to take out the last traces ; so 9 grams of the foil was converted 
into “black,” ignited in air, and placed in a U-tube kept in boiling water, according 
to Hempel’s directions in the methane experiments. 
To remove the air from the Gladstone and Tribe apparatus, a little dry alcohol was 
put in, and it was then connected with a water pump and warmed till nearly all the 
alcohol had boiled away, but the large volume of the apparatus, the great absorbing 
power of alcohol for air and other gases, and the long train of purifying apparatus 
required, must be taken as the excuse for the large percentage of air present. 
Two analyses and the calculation of the result are given in full for the first experi¬ 
ment. 
