The Chemical Relations of Water 289 



soon be fused together. Allow the gas to pass through 

 the jet for about a minute and then collect a sample 

 of it by placing a small ignition tube over the jet, 

 the tube being held in an upright position. The 

 hydrogen rises to the top of the tube and the air is 

 gradually displaced downward. This method of col- 

 lecting a light gas is called "collection by downward 

 displacement of air". When the tube has been in 

 position for several seconds, test the freedom of the gas 

 collected from admixture with air by removing it and 

 lighting it. If it burns quietly, the gas issuing from 

 the jet may be safely lit. Place the jet beneath the 

 bottom of a retort through which cold water is 

 continually circulated f rom . the tap. (See Fig. 95.) 

 The water produced at the high temperature of the 

 flame is naturally in the form of steam. The cold 

 surface of the retort causes part of this steam to be 

 condensed as small drops of water on the exterior of 

 the retort. By continued burning, enough water will 

 be thus condensed to form a large drop at the lowest 

 point of the retort and this may be caught, when it drops, 

 in a clean porcelain dish. To obtain enough water 

 by this means for the performance of several tests is 

 a lengthy process. The simplest plan is to collect 

 about 10 drops in the dish and to apply a test which is 

 applicable to water alone. Dried copper sulphate is 

 a powder of a white or faintly bluish-white colour. 

 Drop a small quantity of this substance into the liquid 

 in the dish. The production of an immediate blue 

 coloration is sufficient evidence that water is contained 

 in the liquid formed by the combustion of the hydrogen. 

 To prove that it is pure water requires further tests to 

 be done. 



Hydrogen + oxygen = hydrogen oxide. 

 H. D. s. 19 



