26 



after equalisation of pressure in both limbs, carefully marked. 

 Electric sparks are then passed for some minutes between 

 the two platinum wires ; the high temperature of the spark 

 decomposes the gas, which expands to exactly double its 

 original volume. Then the voltaic current from five or six 

 cells of a Grove's battery is passed through the spiral of 

 platinum wire, so as to ignite some included pieces of cupric 

 oxide. The hydrogen is thus gradually removed, and nitrogen 

 alone is left to the amount of one-half in bulk of the ammonia 

 originally taken. Hence it is proved that two volumes of 

 ammonia gas are composed of one volume of nitrogen and three 

 volumes of hydrogen. In noting the volumes, the level of the 

 mercury must be equalised in both limbs of the tube. 



112. Apparatus for the decomposition of marsh-gas. 

 E. 57. 1874. 



A convenient volume of marsh-gas is introduced into the closed 

 end of the tube, and, after equalising the pressure, its bulk is 

 marked. It is then decomposed by sparks from an induction 

 coil, with an occasional reversal of the current. Carbon is 

 deposited upon the platinum terminals, and the gas, after decom- 

 position, occupies double its original volume. This product of 

 decomposition can be shown to be hydrogen by igniting it at the 

 jet, when it burns with a flame, which is, however, more or less 

 luminous, on account of the formation of a small quantity of 

 acetylene during the process of decomposition. 



113. Apparatus for showing when carbon or sulphur 

 burns in oxygen no alteration of volume takes place. 



E. 58. 1874. 



This consists of a U-tube with a bulb blown in one limb, capable 

 of being closed with a stopper, through which are passed copper 

 wires sustaining a deflagrating ladle of bone-earth to contain 

 charcoal or sulphur, which may be ignited by the transmission of 

 a galvanic current through a fine platinum wire. The bulb being 

 filled with dry oxygen, and the level of the mercury being 

 marked, ignition of the charcoal or sulphur is effected, and on 

 the cooling of the gas it will be observed that no change of 

 volume has occurred on conversion of oxygen into carbon or 

 sulphur dioxide. 



114. Ozone apparatus. 

 E. 59. 1874. 



This is intended to ozonise oxygen by induction. It 

 consists of a glass tube coated outside with tinfoil ; within 

 this is placed a narrower tube lined with tinfoil or silvered 

 inside. The two metallic coatings are connected with the 

 two ends of the secondary wire of an induction coil, and 

 while a " silent discharge " is made to pass between the two 

 tubes, a current of dry oxygen is slowly driven through from a 

 gasholder. A portion of the oxygen is converted into ozone, 

 which can be detected by means of iodised starch paper at the 



