KEEPING THE IKON COOL. 301 



would begin to melt or burn pretty soon. You see, if the 

 butt end of the barrel was in the burning coals, the muzzle 

 end would get quite hot in a very short time." 



" Certainly," replied Lawrence, " unless we devised some 

 way to keep it cool. There are a great many practical dif- 

 ficulties of this kind to be encountered in making chemical 

 experiments, and it requires sometimes a good deal of in- 

 genuity to contrive means to surmount them. That is one 

 reason why making chemical experiments is so useful to a 

 boy so soon as he- is old enough for such work. It sharp- 

 ens his wits. 



" As to keeping the end of the gun-barrel cool," contin- 

 ued Lawrence, " there is a simple mode of doing that. We 

 have only to wrap the outer end of the barrel, where the 

 India-rubber tube joins it, 'with a strip of cotton cloth, 

 winding it round and round in the form of a bandage, and 

 then keeping the cloth wet by pouring on a little water 

 from time to time out of a pitcher." 



" Yes," replied John, " that would keep it cool." 



" Water has a wonderful power to keep any thing cool," 

 said Lawrence, " even though it is hot water." 



" That is very strange," said John. 



" I mean," said Lawrence, " to keep any thing from get- 

 ting very hot red hot, or hot enough to melt or bum 

 India-rubber, for example; for, before the iron around 

 which the wet cloth is bound becomes hot enough for that, 

 it will be hot enough to boil the water, and water absorbs 

 such an enormous quantity of heat in boiling as to keep 

 the temperature of the iron down to a comparative low 

 point. Of course, as fast as the water in the cloth is boiled 

 and converted into steam, you must pour on more, so as to 

 keep the cloth all the time wet." 



u That would be a great deal of trouble," said John. 



" Yes," replied Lawrence, " and there would be a great 



