76 ANNUAL OF SCIENTIFIC DISCOVERY. 



handles to any room which it is intended to warm. The temperature of 

 the room is increased several degrees by the use of this cylinder, which, of 

 course, gives out neither smoke nor smell, and at the end of five hours 

 the heat in. the cylinder is still so great that the temperature of the room 

 is very nearly what it was when the cylinder was first introduced. This 

 fact is hardly credible, but the experiment has been made several times 

 with the same result. If more than one cylinder be wanted, the genera- 

 tor remains over the fire, and other cylinders can be attached to it, and 

 successively removed. The economy, convenience, and wholesomeness 

 of this mode of heating may readily be conceived. The cost of an ordi- 

 nary apparatus complete does not exceed twenty-five francs, and the only 

 part of it subject to wear and tear is the generator, which does not cost 

 one franc. If meat is to be boiled or stewed, a cooling vessel is attached 

 to the cylinder. When the meat is cooked this is withdrawn, and the 

 cylinder can be detached for the purpose of heating a room. This appa- 

 ratus appears to be admirably calculated for railroad and other carriages, 

 as a small cylinder will for several hours give warmth without an 

 unwholesome emanation of any kind. 



ON THE RE-CUTTING OF THE TEETH OF FILES. 



The following method of re-cutting, or renewing the teeth of old files, 

 has been patented by Edward Gilbert, of London. The teeth are renewed 

 by a corrosive agent applied to the surface of the file. The files are first 

 cleaned from any superabundance of greasy matter, and then placed in a 

 rack inside a bath composed as follows : With one pound of unslaked 

 lime mix two pounds of potash in one gallon of water, stir the whole inti- 

 mately together, allow it to remain till three-fourths the liquid have passed 

 off by evaporation, draw off the remaining quarter of a gallon of liquor, 

 and allow it to cool. In this liquor the files are to remain four hours, and 

 are then to be removed and brushed, cleaned in clean water and made 

 quite free from grease, and then immersed in a vertical position in a mix- 

 ture of one part of sulphuric acid, diluted with two parts of water. The 

 biting action of the acid attacks the whole surface of the files immersed ; 

 the continued effect of which is to deepen the several cavities between the 

 cutting points of the teeth, which become as sharp as they were originally. 

 The files must be immersed for from three to six hours or upward, accord- 

 ing to the fineness of the files and the strength of the liquid. The files 

 must be withdrawn and brushed from the oxide formed five or six times 

 during the process. The patentee states that the process is at once com- 

 paratively inexpensive, and removes so little metal that it may be repeated 

 three or four times on the same file, and thus it will render it advantageous 

 to wear files rrmch less than usual before renewing. 





