THAT STEAM CAN BE SEEN 



those who have not given special attention 

 to the subject see a cloud of vapor floating away 

 from a locomotive in action, the feeling is irre- 

 sistible that they see the steam which causes 

 the piston to move in the cylinder. This, however, is far 

 from being the case. What they really see is a collection 

 of fine particles of water. If these particles had been in 

 the state of steam they would have been in the form of an 

 invisible gas. 



The truth of this is easily proved. Pour a little water 

 into a thin glass flask or a test tube and plug the mouth 

 with a cork having a small hole passing through it. The 

 hole should not be more than an eighth of an inch in diam- 

 eter. Heat the water in the flask or test tube over a spirit 

 lamp or gas flame until the steam rushes out of the hole 

 in the cork with some force. The flask or test tube, al- 

 though filled with steam, will be quite transparent; the 

 steam will not be visible. 



Or watch a jet of steam issuing from the cock of a steam 

 boiler or the spout of a teakettle when the latter is boiling 

 briskly; as the steam issues from the cock or jet it will be 

 quite invisible for a short distance, but when cooled a little 

 by contact with the air it becomes vapor and is easily seen, 

 but then it is not steam. 



196 



