32 THE WORLDS LUMBER ROOM. 



wet patches are sometimes found in the middle of its 

 columns, and as all water contains dissolved oxygen,* 

 wherever water penetrates, there brown patches of oxide 

 are formed, which crack the rock if they cannot otherwise 

 find enough room. There are many other minerals besides 

 iron with which oxygen unites to form oxides, buf as 

 the results are similar we need not dwell upon them now, 

 and may go on to consider some of Nature's other 

 labourers. 



One of the most active of these, even chemically 

 considered, is water, for though we call many substances 

 insoluble, gold and platinum are probably the only two 

 which are actually unaffected even by pure cold water. 

 One sometimes hears people say that china and glass 

 grow thin by repeated washing, and though their senses 

 must be remarkably keen if they are able to detect the 

 change, there is, no doubt, the proverbial grain of truth 

 in what they say; for, if water be kept boiling in a glass 

 vessel for any length of time, it does certainly dissolve 

 some of the glass, while powdered glass at once gives a 

 perceptible flavour even to cold water, and certain kinds 

 of Chinese porcelain have been proved to be more or 

 less soluble. 



But we are speaking of pure water, whereas, from the 

 very nature of the case, it is impossible that there should 

 be any such thing as perfectly pure water, either in the 



* It is this dissolved oxygen, not that combined with the hydrogen, 

 which fishes breathe. If you remove the combined oxygen, water ceases 

 to be water, but you may expel the dissolved oxygen and other gases by 

 boiling, and the water merely becomes " flat. 1 ' 



