Polytechnic Association Proceedings. 84X 



made by the Leblane process, which is sulphate of soda, is dissolved, 

 {Uid it" it shows acid, is neutralized by a solution of lime; soda ash, 

 equal in weight to twelve per cent of the salt cake, is then added 

 to the solution. After the liquid has settled it is drawn off, and 

 large, hard crystals are formed, which may be made still larger by 

 increasing the quantity of soda ash. One ton of salt cake will 

 make neai'ly two tons of the adulterated article. 



THE PALL OF LEAVES. 



M. Fr^cut, in a paper presented lately at the French Academy, 

 calls attention to the phenomenon that occurs just before the fall 

 of the leaf, and which is not unlike the process which accompanies 

 the shedding of horns in animals. It consists in the obstruction 

 of the vessels- at the base of the petiole or foot-stalk, which is 

 effected by the multiplication in the parietes of the vessels until 

 they are completely choked up in the neighborhood of the inser- 

 tion of the leaf, although the other portions of the vessels retain 

 their normal condition. 



PErPER's GHOST. 



This spectral appearance, produced by a transparent mirror in a 

 sliding frame, partially reflecting the rays of a strong Hare light 

 thrown on the person who, beneath the stage and out of sight, 

 plays the part of the ghost, and which for several years in London 

 and one season in New York attracted large houses, has been of late 

 the subject of an angry controversy in Hie London Mechanics^ 

 Magazine. From it we learn that Mr. Henry Dircks, and not Mr. 

 Pepper, is the inventor of the mechanical combination for producing 

 an optical illusion on the stage, like that which may be seen on a 

 large scale in the splendid window panes of Broadway, under a 

 mid-day sun. 



HOSE COUPLING. 



"VY. H. Haight exhibited Mr. Gifford's hose coupling, which obvi- 

 ates the use of a screw. This coupling has on one of its pieces a 

 slot and inclined plane into which a projection on the other piece is 

 inserted. By means of the inclined plane the parts of the coupling 

 are 1)rought together with any desired closeness. The whole work 

 of uniting the coupling is done by one motion and without turning 

 the parts once around. The advantage claimed for it is expedition 

 and the certainty of a tight fit. The coupling has stood a pressure 

 of 950 pounds per square inch. 



Dr. Adolph Ott read the following paper: 



