ON SUPERHEATED STEAM. 201 



much to get the atmosphere of steam from the 

 plaster, as it is beautifully simple and self-regu- 

 lating. If water be used at all, the quantity never 

 should exceed a gill, as the safety of having an 

 atmosphere of steam only to be heated, would not 

 be secured. I do not now advise putting any 

 water at all to get the atmosphere of steam, as it 

 has happened, as I thought it would, that the 

 instructions to put only a certain small quantity 

 of water in are so liable to be neglected, and bad 

 results follow. There is perfect safety if those 

 who use it will clearly bear in mind that an 

 atmosphere of steam only is wanted; this im- 

 portant fact, if once fixed in the mind, will never 

 go out of it. The . use of a boiler requires care, 

 and is like walking along a narrow plank over a 

 fall 1,700 feet from the ground ; the use of a 

 steam-chamber is like walking along a plank one 

 foot from the ground : in the case of a slip, the 

 difference of danger is too evident to require 

 comment. With a chamber filled with steam only, 

 the heat radiates through all parts of it, and is a 

 great advantage, as one part of the vessel cannot 

 get so very much hotter than another, and the 

 bottom cannot be made red-hot with gas coils, as 

 it is liable to be with water and its earthy deposits. 

 With steam only being present, not so much sul- 

 phuretted hydrogen is formed as when water or 

 air is used, as is well known to those who have 

 had practical experience in the matter, but more 



