116 NUTRITIVE PLANTS. 



is set down on a table, and it supports it in such a manner that the 

 bottom of the boiler is elevated to the height of half an inch above 

 the table. 



" When the boiler is heated over a spirit lamp, or over a small 

 portable furnace in which charcoal is burnt, as the vapour from the 

 fire will pass off through the holes made in the sides of the hoop, 

 the bottom of the hoop will always remain quite clean, and the table- 

 cloth will not be in danger of being soiled when this coffee-pot is 

 set down on the table. 



'* As the hoop is in contact with the boiler, in which there will 

 always be some water, it will be so cooled by this water as never to 

 become hot enough to burn the table-cloth. 



" The bottom of the boiler may be cleaned occasionally, on the 

 underside, with a brush or a towel ; but it should not be made 

 bright ; for when it is bright it will be more difficult to heat the 

 water in it than when it is tarnished and of a dark-brown colour. 



But the sides of the boiler should be kept as bright as possible ; 

 for, when its external surface is kept clean and bright, the boiler will 

 be less cooled by the surrounding cold bodies, than when its me- 

 tallic splendour is impaired by neglecting to clean it*. 



" As the small quantity of water which is put into the boiler serves 

 merely for generating the steam which is necessary in order to keep 

 the reservoir and its contents constantly boiling-hot ; if the reservoir 

 be made of silver, or even of common tin, the boiler may, without 

 the smallest danger, be made of copper ; or of copper plated with 

 silver, which will give to the boiler an elegant appearance, and at 

 the same time render it easy to keep it clean on the outside. 



" The boiler may likewise be made of tin, and neatly japanned on 



*' I have in my possession two porcelain tea-pots, of the same form and di- 

 mensions, one of which is gilt all over on the outside, and might easily be mis- 

 taken for a gold tea-pot; the other is of its natural white colour, both within 

 and without ; being neither painted nor gilt. When they are both filled at the 

 same time with boiling water, and exposed to cool in the same room, that which 

 is gilt retains its heat half as long again as that which is not gilt. The times 

 employed in cooling them a given number of degrees, are as three to two. 



" The result of this interesting experiment (which I first made about seven 

 years ago) affords a good and substantial reason for the preference which Eng- 

 lish ladies have always given to silver tea-pots. The details of this experiment 

 may be seen in a paper published in the Memoirs of the French National Insti- 

 tute for the year 1807." 



