12 



the volume of the enclosed gas may be at once read off*. A 

 horizontal pointer is also provided for getting the mercury 

 accurately level in both tubes. 



76. Hofmann's apparatus for showing the synthesis 

 of water. 



Made by J. Schober, Berlin. 

 E. 263, 264, and 265. 1877. 



These instruments consist of U -tubes, with one closed and one 

 open limb ; two of the instruments having the former provided 

 with a stopcock. All have platinum terminals. 



They are used in exactly the same way as the above, but 

 unless the closed limb is surrounded by a jacket the steam will 

 condense, any excess of either gas (oxygen or hydrogen) above 

 the combining proportions being left. 



77. Hofmann's apparatus for decomposing phos- 

 phuretted hydrogen. 



E. 258. 1877. Made by J. Schober 9 Berlin. 



This apparatus consists of a U-tube, one limb being sealed and 

 provided with two carbon points to be connected with a battery. 

 The open limb is provided with a stopcock at the lower end. 



The apparatus is used in the same way as the one for de- 

 composing ammonia, two vols. of phosphuretted hydrogen liberat- 

 ing three vols. of hydrogen, the phosphorus being deposited as 

 a brown powder on the sides of the tube. Carbon points are 

 used, as the liberated phosphorus is apt to combine with the 

 hot platinum to form a fusible compound. 



78. Hofmann's apparatus for decomposing ammonia 



gas. 



E. 256. 1877. Made by Julius Schober -, Berlin. 



This apparatus consists of a U-tube, with one limb terminating 

 in a narrower tube, and closed with a stopcock, the other limb 

 being open and fitted with a tap near the bend of the limb. The 

 closed limb is fitted with two platinum wires fused into the 

 glass near the top, and nearly meeting inside. These are to be 

 connected by the outside loops with the terminals of a battery. 



The sealed limb is filled to about one-third of its height with 

 dry ammonia, and the volume of the gas measured by bringing 

 the levels of the mercury in the two limbs into coincidence. A 

 series of electric sparks is now passed between the wires. The 

 volume of the gas immediately increases, and in about 10 or 

 15 minutes, after adjusting the level of the mercury, the volume 

 will have become doubled. By allowing a little gas to escape 

 the odour of the ammonia will no longer be perceptible, and the 

 hydrogen will inflame. This experiment shows that if we could 

 make three vols. of hydrogen combine with one vol. of nitrogen 

 we should obtain two vols. of ammonia. 



