242 REPORT— 1889. 



the dried ^ gas is burnt at a jet underneath a Florence flask through 

 ■which a stream of cold water is allowed to circulate : the neck of the 

 flask is passed through the neck of a bell jar and the flask and bell jar 

 are clamped up in an inclined position, so that the liquid which con- 

 denses may drop into a small beaker placed below the rim of the jar. 

 What is the liquid ? It looks very like water, and is without taste or 

 smell. Is it water ? How is this to be ascertained ? What are the 

 properties of water ? The knowledge previously gained here becomes of 

 importance. It has been observed that frozen water melts at 0° Centi- 

 grade, that water boils at 100°, and that one cubic centimetre weighs one 

 gramme at 4° C. ; so the liquid is frozen by the ice-maker's mixture of 

 ice and salt, a thermometer being plunged into it so that the solid ice 

 forms on the bulb : the melting-point is then observed. Subsequently the 

 boiling-point is determined, a little cotton- wool being wrapped around the 

 bulb of the thermometer. Lastly, the density of the liquid may be 

 determined. It is thus established that the gas yields water when 

 burnt, and the name of the gas may now for the first time be mentioned 

 and explained. The results thus obtained leave little doubt that water 

 is an oxide of hydrogen ; but in order to place this beyond doubt it is 

 necessary to exclude nitrogen altogether. How is this to be done ? Red 

 lead is known to consist of lead and hydrogen only, and readily parts with 

 a portion at least of its oxygen ; so dried hydrogen is passed over red lead, 

 which is then gently heated. Again a liquid is obtained which behaves 

 as water, so there can be no doubt that water is an oxide of hydrogen. 

 Water is not obtained on merely mixing oxygen and hydrogen ; it is only 

 produced when combustion takes place. To start the combustion a flame 

 is applied to a small quantity of a mixture of the two gases : a violent 

 explosion takes place. An opportunity is here again aiJorded of calling 

 attention to the entire change in properties which takes place when the 

 compound is formed. On heating red lead in hydrogen, lead is obtained, 

 although on heating it alone it loses only a portion of its oxygen, and 

 the ' reduction ' takes place very readily ; evidently, therefore, hydrogen 

 is a powerful agent. This observation suggests further expei-iments. 

 Will it not be possible to remove oxygen by means of hydrogen from 

 other oxides which are not altered on heating ? and will not other 

 combustible substances besides hydrogen remove oxygen from oxides ? 



PROBLEM X. To determine what happens when hydrogen and other com- 

 hustible substances are heated with oxides. — Zinc oxide, iron rust and 

 copper oxide ai'e now heated in a current of hydi'ogen : the first remains 

 unaltered, the other two are seen to change, a liquid being formed which 

 it cannot be doubted is water ; the copper oxide evidently becomes 

 reduced to copper. Is the iron rust similarly reduced to the metallic 

 state ? How is iron to be tested for ? Iron is attracted by the magnet, 

 and dissolves in diluted oil of vitriol with evolution of hydrogen. Apply- 

 ing these tests, no doubt remains that the iron rust is deprived of its 

 oxygen. 



Litharge and copper oxide may then be mixed with soot or finely 

 powdered charcoal and heated in tubes ; gas is given oS" which renders 

 lime water turbid, and metallic lead or copper is obviously obtained. It 

 is thus estabhshed that some but not all oxides may be deprived of 



* The importance of dryinCT the gas is realised without difficulty, as previous 

 observations have shown that the air is moist, and as the gas is given ofE in presence 

 of water ; lime may be used. 



