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FARADAY 



action of water, and then to apply that test to what Is col- 

 lected as a drop at the bottom of that vessel. I have here a 

 chemical substance, discovered by Sir Humphrey Davy, 

 which has a very energetic action upon water, which I shall 

 use as a test of the presence of water. If I take a little 

 piece of it it is called potassium, as coming from potash- 

 if I take a little piece of it, and throw it into that basin, you 

 see how it shows the presence of water by lighting up and 

 floating about, burning with a violet flame. I am now 

 going to take away the candle which has been burning 

 beneath the vessel containing ice and salt, and you see a 

 drop of water a condensed product of the candle hanging 

 from the under surface of the dish. I will show you that 

 potassium has the same action upon it as upon the water 

 in that basin in the experiment we have just tried. See! 

 it takes fire, and burns in just the same manner. I will take 

 another drop upon this glass slab, and when 

 I put the potassium on to it, you see at once, 

 from its taking fire, that there is water 

 present. Now that water was produced by 

 the candle. In the same manner, if I put this 

 spirit-lamp under that jar, you will soon see 

 the latter become damp from the dew which 

 is deposited upon it that dew being the 

 result of combustion; and I have no doubt 

 you will shortly see, by the drops of water 

 which fall upon the paper below, that there 

 is a good deal of water produced from the 

 combustion of the lamp. I will let it remain, 

 and you can afterward see how much water 

 has been collected. So, if I take a gas-lamp, 

 and put any cooling arrangement over it, I shall 

 get water water being likewise produced from the com- 

 bustion of gas. Here, in this bottle, is a quantity of water 

 perfectly pure, distilled water, produced from the combus- 

 tion of a gas-lamp in no point different from the water 

 that you distill from the river, or ocean, or spring, but 

 exactly the same thing. Water is one individual thing; it 

 never changes. We can add to it by careful adjustment 

 for a little while, or we can take it apart and get other 



