648 THE POPULAR SCIENCE MONTHLY. 



gun out. If it be desired to let the gun run out automatically imme- 

 niately after recoil, it is only necessary to leave the running-out cock 

 F open, and then the water forced among the cork by recoil returns 

 instantly to the cylinders, and runs the gun out quicker than the eye 

 can follow the motion. 



The arrangement adopted may be made by using air instead of 

 cork, but air is a troublesome substance to deal with ; it leaks out 

 very easily and without showing any signs of having done so, which 

 might readily lead to serious consequences. A special pump is re- 

 quired to make up loss by leakage. 



The merit of cork is its extreme simplicity and trustworthiness. 

 By mixing a certain proportion of glycerine with the water it will not 

 freeze in any ordinary cold weather. 



Each of the applications of cork is based on some of the physical 

 or chemical properties of the substance. In bottle-corks its imper- 

 meability, elasticity, and imputrescibility are brought into service. 

 Its lightness, the first quality that strikes us, on a superficial view, 

 is not considered. 



Cork is used for a variety of other purposes than those which 

 have been mentioned, which, while not so economically important as 

 these, still deserve attention. The male cork, while not well adapted 

 for stoppers, has been made available in the decoration of parks and 

 gardens. Rice-hulling mills have been made from it, but not with 

 much success ; small corks can be got out of it. Water-conduits and 

 bee-hives have been constructed from it. It furnishes excellent damp- 

 proof shelves and stands. The Kabyles employ it, mixed with a 

 mortar of mud, in building the walls of their houses, and shingle 

 their roofs with it. It is used for the floats of fish-nets. 



These various applications were known, as w T e learn from expres- 

 sions of Theophrastus and Pliny, to the Greeks and Romans. Pliny 

 says : " Only that bark is used that is thick and springs back when it 

 is pulled. It is sometimes employed for the buoys of ships' anchors, 

 fishermen's nets, barrel-bungs, and women's winter sandals. The 

 Greeks felicitously called the cork-oak the bark-tree. Cork is used for 

 the covering of roofs." The chips form a good non-conducting ma- 

 terial for keeping ice, and reduced to fragments make excellent stable- 

 floors and race-course tracks. 



The real, or female cork, has a more homogeneous grain and works 

 much better than male cork. It is a very poor conductor of heat and 

 sound, and has been found valuable to protect hot surfaces against 

 cooling, and to keep frigid substances from melting. It is the basis 

 of several non-conducting mastics and coverings, which are used for 

 protecting pipes, steam-boilers, hot-water reservoirs, etc. Three meth- 

 ods of applying the cork-covering are employed in France. Strips of 

 cork touching at their edges may be laid along the pipes and cylinders 

 and drawn together by wire as in No. 1, Fig. 9. The pipe clothed in 



