=Picric Acid.= When coal tar is subjected to a fractional distillation the portion which comes over up to a temperature of 170 deg. C. is called “light oil” and contains all the compounds of low boiling paint contained in tar, and from this several of our most valuable explosives can be obtained. When these light oils have distilled over the next fraction, or “middle oil,” yields phenol or carbolic acid, a body which nitrated gives picric acid, which is the basis of the French high explosive “melinite” and the English “lyddite.” Picric acid consists of a very strong nitric acid and carbolic acid, and is a very high explosive. It was introduced by Turpin, who mixed it with collodium and called it “melinite,” by which name it is known in the French Service. It forms with metals a class of salts (picrates). The potassium salts were suggested as a bursting charge for shells nearly fifty years ago. Sprengel and, later, Turpin, employed the acid itself as an explosive. It was possible to get a great weight of explosive into small space, as the acid could be melted and poured into the shell in a molten condition. Picric acid is a very safe explosive, but has the drawback of acting on metals, forming “picrates,” some of which are more sensitive to disturbing influences than the acid itself. =Lyddite.= Lyddite consists of melted solidified picric acid, and has the same disadvantage of forming “picrates” when in contact with metal, making it necessary to varnish the interior of shells when used in them. Experience with lyddite shells shows them to be very erratic, due to the fact that they require a very powerful detonator, the use of which is very dangerous, as they may cause a premature explosion. =T. N. T.= These disadvantages in picric acid led to its being largely replaced by tri-nitro toluol, or T. N. T., which has a bursting pressure of 119,000 pounds per square inch as against 135,820 pounds for picric acid. Yet the advantages of the former more than compensate and warrant its use being preferred. T. N. T. does not act on metals to create sensitive salts and is, therefore, perfectly stable. The French name for T. N. T. is “Tolitype,” the Spanish “Trilite,” and the German “Trotyle.” It is produced by heating troulue with a mixture of nitric acid and sulphuric acid. =Troulue.= Troulue is a liquid hydro-carbon obtained along with benzine. =Tetryl.= Tetryl is another coal tar product containing more nitrogen than lyddite, and is employed in detonators with a little lead azide, making a less sensitive and safer preparation than fulminate of mercury. =Aunnonal.= Aunnonal is a mixture of T. N. T., aluminum in fine powder and nitrate of ammonia, and a trace of charcoal. It is safe and powerful, but has the disadvantage of attracting moisture, and for that reason does not always explode.