MECHANICS AND USEFUL ARTS. 51 



very readily acted upon by damp, and is rusted in a short time, either 

 by decomposing the water and obtaining oxygen from that source, or 

 direct from the atmosphere. It is not absolutely essential that the 

 quicklime should be in actual contact with the metal, but if some- 

 where near, as in the case of the parcel of lime packed up with the 

 needles or watchsprings, the bright metal will remain a long while 

 without the least alteration in its appearance ; the lime (which is al- 

 ready an oxide of calcium) , either receiving an additional dose of oxy- 

 gen, or being converted into a carbonate of lime. Mr. C. II. Smithy 

 in Builder. 



New Process for coating Metals. At a recent meeting of the 

 French Academy, a communication was read by M. Weil, "On New 

 Processes for Covering Metals with Firmly Adherent and Bright Lay- 

 ers of other Metals." The method consists in dipping the metal to be 

 coated in a saline solution of the metal to be deposited, rendered dis- 

 tinctly alkaline with potash or soda, and mixed with some organic "mat- 

 ter, such as tartaric acid or glycerine. At the same time, it is neces- 

 sary in some cases to set up a weak voltaic current by keeping a piece 

 of zinc or lead in contact with the metal. In this way the author ob- 

 tains a firm layer of copper, or iron and steel, and procures various 

 and beautiful effects according to the thickness of the copper depos- 

 ited. Silver, nickel, and other metlas can be applied in the same way. 

 The process, it will be seen, is susceptible of numerous applications. 

 A curious fact mentioned is that a clean surface of copper may be 

 coated with zinc by placing the two metals in contact, in a solution of 

 caustic soda or potash. In the cold the deposit of zinc takes place 

 slowly, but at 100 it is effected rapidly. 



ON THE PRESERVATION OF WOOD. 



The following composition is recommended to protect the bottom of 

 posts, palings, and tubs set in the earth: 40 parts of chalk are add- 

 ed to 60 parts of resin, and four parts of linseed oil, melted togeth- 

 er in an iron pot. One part of. native oxide of copper is then added, 

 and one part of sulphuric acid is cautiously stirred in. The mixture 

 is applied hot with a strong brush, and forms, when dry, a varnish as 

 hard as stone. London Chemical News. 



Preservative Action of Sulphate of Copper on Wood. The exper- 

 iments of M. Konig have demonstrated that the sulphate of copper 

 deprives wood of the nitrogenous matter which acts as a ferment, this 

 matter being found in the solution of the copper. At the same time a 

 combination of resin and copper is formed, which closes up the pores 

 of the wood and preserves it from the action of the air. The wood, 

 however, is still susceptible of decomposition, in consequence of the 

 variations of temperature and humidity. M. Weltz, while occupied 

 with the solution of the last questions, has arrived at the following 

 conclusions : He has remarked that the wood gradually blackens as 

 the layers of metallic copper are produced on it. The sulphate of 

 copper is fixed in the wood : this salt decomposes itself into metallic 

 copper and sulphuric acid. The latter chars the wood, and it is 

 through this layer of charcoal, the preserving agency of which has 

 been so often remarked, that the wood is enabled to resist the action 



