of Porcelain, Gilded and not Gilded. 243 



the cooling (or heating) action of surrounding bodies, 

 is too evident to need much explanation. Since, in 

 household economy, use is often made of porcelain ves- 

 sels for holding warm liquids, which it is desired to 

 keep warm for a long time, as, for example, tea, 

 coffee, etc., in all such cases it would be of advantage 

 to use vessels gilded on the outside ; or, if gilding be 

 found too expensive, it is possible to use, and with 

 equal advantage as regards retaining the heat, vessels 

 which are silvered or covered with a layer, no matter 

 how thin, of any other metal not liable to be readily 

 oxidized in the air. 



As to gilding the vessels on the inside, it would be 

 to no purpose, for it would add nothing to the effect in 

 question, as I have learned from the results of several 

 experiments. This, however, applies only to simple 

 vessels ; for in case a double vessel were employed in 

 order to retain more effectually the heat of any sub- 

 stance, the outside vessel must be gilded on the inside 

 as well as on the outside ; in no case is it necessary for 

 the inner vessel to be gilded on the inside. 



If it is a question of preserving the low temperature 

 of liquids or other cold substances, such as ice-creams, 

 etc., in this case, also, vessels having externally a polished 

 metallic surface should be used ; for a surface of this 

 description throws off by reflection a large portion of 

 the calorific rays which reach it from surrounding 

 objects, and consequently the vessel grows warm very 

 slowly. 



Everybody knows how much time it takes to bring 

 water to boiling in a silver coffee-pot which is clean and 

 bright on the outside, especially before an open fire, or 

 on glowing coals which burn without smoke. It is, 



