162 Miscellaneous Intelligence. 



a great part of the liquid being allowed to evaporate, the 

 mixture begins to change from black to brown, and then 

 quickly to red. No more water is to be added, but the tritu- 

 ration is to be continued. The mass will acquire the con- 

 sistence of a jelly, and the red becomes more and more bril- 

 liant with great rapidity. When it has attained its highest 

 perfection the cup should instantly be removed from the flame, 

 or the red will quickly change to a dirty brown colour. — Phil. 

 Mag. 



16. Dobereiners Apparatus for maldng Extracts. — This ap- 

 paratus serves to extract by means of water, alcohol or ether, 

 the soluble substances from any substance to be analyzed, in 

 quantities from 10 up to 200 grains. It is composed of a tube 

 of glass from 4 to 9 lines in diameter, and from 4 to 9 

 inches long. The tube is closed below by a cork, to which 

 is adapted a small tube open at both ends. This, except that 

 its upper extremity is covered with a piece of muslin, commu- 

 nicates with the large tube. The substance to be operated 

 upon is put into the large tube about half filling it, and the 

 solvent is then put in over it. A small glass bulb propor- 

 tionate in size to the quantity of solvent used, is then emptied 

 of air by heating a few drops of alcohol in it, and immediately 

 attached by a tight cork to the lower end of the small tube. 

 The whole apparatus is then set aside in a cool place ; as the 

 alcohol vapour condenses, a vacuum is produced, and the pres- 

 sure of the air in the large tube forces the fluid through the 

 substance to be operated upon into the bulb. In a hw mi- 

 nutes the extraction is complete, the bulb is then removed, its 

 contents taken out, the air in it again displaced, and the operation 

 repeated ; or, if necessary, the fluid is left in contact with the 

 substance some time before it is made to pass from it into the 

 hnVo.— Bib. Univ. xxi. 188. 



17. Heat from Friction of a Solid and Fluid. — It may be 

 remarked that the rapid rotation of the little mills which com- 

 plete the attenuation of the liquid mixture for paper before it 

 passes to the tub, produces in it a very sensible heat not at all 

 due to the elevation of the temperature of the wheel itself by 

 the friction of its axis, for it cannot be perceived by touching 

 that part, but attributable to the blow of the fans of the wheel 

 on the mixture, which they strike with much rapidity and vio-?' 



