400 Foreign Literature and Science. 



ing it off, and another, for which the first may easily be sub- 

 stituted, for receiving a bent tube which conveys the steam 

 out of doors. The exterior vessel does not rise hioher 



o 



than the interior, but it descends lower and rests upon the 

 grate. 



From an experiment of the reporters, one part of char- 

 coal is sufficient to vaporize 9.42 parts of water from the 

 freezing point. Now, according to theory, charcoal can 

 evaporate only 10.8 times its own weight of water, hence it 

 appears, that, taking into consideration the heat communica- 

 ted to the vessels themselves, the actual loss of heat is only 

 -j\ which is very trifling. 



The superiority of this instrument for culinary purposes, 

 especially for soups, vegetables, he. is attested by these sci- 

 entific reporters, who assert that they intend habitually to 

 use it, as it is attended with an economy of time, and fuel, 

 an improvement in the quality of the food, and a certainty 

 of success. 



46. Salt Petre. — M. Baffi, an able chemist, born at Per- 

 gola, has received from the Vice Roy of Egypt, a present 

 of 100,000 crowns, and the title of Bey, for having discover- 

 ed a method of making salt-petre by the sun's heat alone, 

 without the aid of fire. Before this discovery every cwt. 

 of salt-petre cost the Vice Roy ten crowns, an expense 

 which is reduced by the new method to one crown. The 

 manufactory erected by M. Baffi on the great plain of Mem- 

 phis furnished last year, to the Egyptian army, 3,580,000 

 lbs. of salt-petre. 



47. Dr. Brewster has published (in the Trans, of the 

 Cambridge Philos. Soc.) an interesting paper on certain 

 peculiarities in the structure and optical properties of the 

 Brazilian topaz illustrated by colored figures: — also (in the 

 Trans, of the R. Soc. of Edin.) a description and drawings 

 of a Monochromatic lamp with remarks on the absorption 

 of the prismatic rays, by coloured media — also an account 

 of the native hydrate of Magnesia discovered by Dr. Hib- 

 bert in Shetland, and, in a separate pamphlet, additional ob- 

 servations on the connexion between the primitive forms of 

 minerals and the number of their axes of double refraction. 

 Dr. Brewster's researches on the optical properties of min- 

 erals continue to present very extraordinary results. 



