CORK, ITS MANUFACTURE AND PROPERTIES. 639 



may be desired. The conical corks are used when the corking is done 

 by hand, the cylindrical ones when it is done by machinery. Other 

 machines for punching corks into shape and for grinding them have 

 been tried and discarded. M. Moreau, the inventor of the latter ma- 

 chine, combined with it the idea of cutting a portrait-face on the cork, 



Fig. 2. Cork-Square Cutting-Machine. 



so that every house might send out the image of its chief on its wares ; 

 but the device has not advanced further than to the stage of a happy 

 thought. Another machine has been invented in which the knife is a 

 rotating disk, self -sharpening, and the cork also turns. 



After having been shaped, the corks are washed in water containing 

 oxalic acid or chloride of tin, or are sometimes treated with sulphuric 

 acid. They thus acquire a characteristic salmon tint, and become vel- 

 vety and soft to the touch. They are then sorted according to size, 

 tested for quality, counted by hand or by the aid of special machines, 

 and packed in sacks containing from fifteen to thirty thousand each. 



The quality most sought in a good cork is impermeability to gases 

 and liquids. The bark may be tested for this quality before making 

 up, by means of an apparatus invented by M. Salleron, in which it is 

 subjected to the pressure of a liquid which has already been com- 

 pressed in a hydraulic machine. A cork of the first quality should 

 stand a pressure of several atmospheres without absorbing any of the 



