PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 595 



drying cement is made by mixing' equal weights of such gum, lime 

 and minium (red lead). Gutta-percha, dissolved by chloroform, 

 produces a cement now used for holding together pieces of leather. 

 The mixture is spread on the pieces to be joined, and allowed to 

 dry, after which they are warmed and pressed together. This 

 cement, although water-proof, will not resist any great strain, but 

 will be found serviceable in covering many small defects ; for 

 instance, those arising from wearing high-heeled boots, the hiding 

 of which was the origin of the now fashionable toe-pieces. Gutta- 

 percha soles can thus be attached to new boots, which may last for 

 a winter. There are doubtless many other ugfes to which the gum 

 cements described may be applied with advantage. 



Cement foe Rooms. 

 M. Sarel, of Paris,> uses a coating for walls which is said to be 

 sujDerior to pure gypsum. The oxide of zinc is mixed with size, 

 made up like a Avash, and applied to a wall, ceiling, or wainscot. 

 Afterwards the chloride of zinc, made into a wash in the same 

 way, is applied. The oxide and chloride immediately combine 

 and form a kind of cement, smooth and polished as glass, and pos- 

 sessing the advantages of oil paint, yet without any objectionable 

 smell. 



Electro-Plating. 

 It is said, on French authority, the addition of a small quantity 

 of bi-sulphide of carbon to the silver and potassium bath, causes 

 the deposit to take place with perfect evenness, and results in the 

 production of a highly brilliant surface on the object plated. 



Work of Ocean Steamers. 

 The wheels of the large ocean steamers make about 200,000 

 revolutions in crossing the Atlantic, between New York and 

 Liverpool. 



VEGETiV.BLE SOAP. 



Mr. Payne recently brought from China to Europe specimens of 

 the vegetable soap used throughout that Empire. It is in the form 

 of pods, produced by two leguminous plants. Before using these 

 pods for washing, the Chinese tirst cut away the greater part of 

 the epicarp, and then rub the wet linen with the pods thus denuded, 

 after which it is enouo;h to rinse the linen in fresh water. 



