378 On the Construction of Kitchen 



made to turn over the top of the brim of the steam-rim 

 of the boiler. 



There may either be a steam-tube in the cover of the 

 boiler, or the steam may be permitted to force its way 

 under the descending rim of the inverted shallow pan 

 which constitutes the cover. If there be a steam-tube, 

 it should be half an inch in diameter and about one 

 inch in length ; and it should be made very smooth on 

 the inside, in order that another tube of tin or of tinned 

 copper, about 10 inches in length, may pass freely in it. 

 The use of this movable tube is to cause the air to 

 be expelled from the upper boiler, while it is used for 

 cooking with steam. This will be done if, while the 

 water below is boiling, the long tube be thrust down 

 into the boiler through the steam-tube till its lower end 

 comes to the level of the brim of the lower boiler. For, 

 as steam is considerably lighter than common air, it will 

 of course rise up and occupy the upper part of the upper 

 boiler, and the air below it being compressed will escape 

 through the tube we have just described ; and, although 

 that tube should remain open, the upper boiler will 

 nevertheless remain filled with steam, to the total exclu- 

 sion of atmospheric air. The inside of the steam-tube 

 and the outside of the movable tube should be made to 

 fit each other with accuracy, in order that no steam may 

 escape between them. The necessity of this precaution 

 is too evident to require any elucidation. 



It will be best to place the steam-tube within about 

 an inch of the side of the cover, in which case it will 

 be easy, by turning the cover about, to place it in such 

 a position that the movable tube may descend into the 

 upper boiler without being stopped by meeting with 

 any of the dishes that are placed in it. 



