SECT. m. ITS DERIVA TI VES. 1 2 1 



carbons. The carbolic and cressylic acids are the most 

 important of these acid oils. The carbolic acid, which 

 has the property of arresting the putrefaction and 

 decay of organic matter, consists of 12 equivalents of 

 carbon, 6 of hydrogen, and 2 of oxygen. The cressylic 

 acid only differs from the preceding by having two more 

 equivalents of hydrogen and two of oxygen in its chemi- 

 cal composition. 



Creosote is a mixture of these two acids. Those vast 

 beams of wood that are driven as piles into the sand or 

 mud at the bottom of the sea, as well as the timbers 

 that form marine superstructures, are saturated with it 

 to a certain depth to preserve them from the attacks of 

 marine insects, especially Limnoria terebrans, an isopod 

 crustacean, which is so destructive in some of our har- 

 bours. The wood is deprived of its air by heat and the 

 creosote easily enters. 



Carbolic acid is liquid, but becomes solid when puri- 

 fied and dried ; and as already mentioned the brilliant 

 yellow dye, carbazotic acid, one of the coal tar colours, 

 is a compound radical, in which the peroxide of nitrogen 

 has replaced three equivalents of hydrogen. The other 

 coal tar colours are obtained from the neutral hydro- 

 carbons, that is to say, compounds of hydrogen and 

 carbon, such as benzol, toluol, and other analogous 

 substances. 



Benzol, which consists of 12 equivalents of carbon and 

 6 of hydrogen, is very volatile, boiling at 117 Fahr., and 

 when acted upon by nitric acid, it forms a compound 

 radicle in which one equivalent of oxide of nitrogen 

 takes the place of one of hydrogen. It smells strongly 

 of bitter almonds, and may be used with safety instead 

 of them. When water and iron are mixed with nitro- 

 benzol, the iron combines with the oxygen and forms 

 oxide of iron, and the result is rusted iron and aniline, 

 which is the origin and foundation of the coal tar 



