THE RAPID AGEING AND FIREPROOFING OF WOOD. 295 



cuiTent employed is 110 volts, but instead of being directed 

 through the wood always in the same direction, a change is made 

 every hour or every two hours, or half the amount of electric 

 horse-power necessary for the operation is passed from the top to 

 the bottom, and then the other half from the bottom to the top. 



The duration of the treatment by electricity is proportioned to 

 the electric resistance of the wood, which varies according to its 

 nature, its thickness and its humidity. As in the processes by 

 injection, the operation is the more prompt and complete, whatever 

 the species of timber, provided it has been recently felled, that is, 

 if the sap has not undergone modification. The time may vary 

 from seven to fourteen hours. 



During the electric treatment there is a formation in the mass 

 of the wood, under the inlluence of the electrolysis, of new mineral 

 compounds, stable and imputrescible, and this in a way much more 

 complete than by any other process, preventing the ulterior 

 development of the germs which cause the decomposition of the 

 wood. The action of the electric current in the process of the 

 ageing of wood is therefore very important. Investigation with 

 the microscope, and the results of analysis, demonstrate the penetra- 

 tion of the action to the heart of the wood. 



Drying of the Treated Wood. — After treatment, if the wood is in 

 logs, it is cut up, according to need. After it has been thoroughly 

 soaked with water, it is left from 8 to 15 days under a shed for 

 drying. For this purpose the boards or scantlings are piled on 

 each other separated by two or more spruce laths, according to 

 length, the thickness of the lath varying from 8 to 25 millimetres 

 {\ of an inch to 1 inch), according to the thickness of the boards. 



If sufficient space is available, the wood can be left to dry 

 entirely in the open air, but it there undergoes alternations of 

 heat and cold. It seems, therefore, preferable, after a first 

 drying without, to pile the timber in a chamber, where a current 

 of heated air is kept in constant circulation for from two to eight 

 weeks, accoidiu^ to thickness, at a temperature gradually increased 

 to 35° or 40° C. (95° or 104° Fahr.). The wood is then thoroughly 

 dried and ready for use. 



Principal Advantages oj the Artificial Ageing of Wood over the 

 Process of Natural Drying. — If a piece of senilised wood and a 

 piece of the same kind simply dried in the open air are compared 

 under the microscope, it will be observed that the cells of the 

 former have undergone contraction. The entrance of air is there- 



