126 FARADAY 



chrough that barrel, if it went through into the water, would 

 be condensed; for you have seen that steam can not retain 

 its gaseous form if it be cooled down; you saw it here 

 [pointing to the tin flask] crushing itself into a small bulk, 

 and causing the flask holding it to collapse; so that if I 

 were to send steam through that barrel it would be con- 

 densed, supposing the barrel were cold; it is therefore 

 heated to perform the experiment I am now about to show 

 you. J am going to send the steam through the barrel in 

 small quantities, and you shall judge for yourselves, when 

 you see it issue from the other end, whether it still remains 

 steam. Steam is condensible into water, and when you 

 lower the temperature of steam you convert it back into 

 fluid water; but I have lowered the temperature of the gas 

 which I have collected in this jar by passing it through 

 water after it has traversed the iron barrel, and still it does 

 not change back into water. I will take another test and 

 apply to this gas. (I hold the jar in an inverted position, 

 or my substance would escape.) If I now apply a light to 

 the mouth of the jar, it ignites with a slight noise. That 

 tells you that it is not steam; steam puts out a fire: it does 

 not burn; but you saw that what I had in that jar burnt. 

 We may obtain this substance equally from water produced 

 from the candle flame as from any other source. When it 

 is obtained by the action of the iron upon the aqueous vapor, 

 it leaves the iron in a state very similar to that in which 

 these filings were after they were burnt. It makes the iron 

 heavier than it was before. So long as the iron remains 

 in the tube and is heated, and is cooled again without the 

 access of air or water, it does not change in its weight ; but 

 after having had this current of steam passed over it, it 

 then comes out heavier than it was before, having taken 

 something out of the steam, and having allowed something 

 else to pass forth, which we see here. And now, as we have 

 another jar full, I will show you something most interest- 

 ing. It is a combustible gas; and I might at once take this 

 jar and set fire to the contents, and show you that it is com- 

 bustible; but I intend to show you more, if 1 can. It is 

 also a very light substance. Steam will condense ; this body 

 will rise in the air, and not condense. Suppose I take 



