142 ANNUAL EEPOET SMITHSONIAN INSTITUTION, 1917. 



the corresponding potential equals 573'^™ which is much in excess of 

 that characterizing the first reaction given above. These reactions 

 correspond in effect to the following: 



The velocity of detonation of cores of melinite inclosed in lead or 

 tin envelopes is about 7,000 meters per second. Dautriche, with very 

 powerful primers, has obtained a velocity of 7,645 meters per second. 



Although the properties of fused picric acid were known before 

 the time of Turpin, yet it is to this inventor we owe its utilization 

 as a military explosive. Turpin has devised that form and dis- 

 position of detonator which has insured its complete detonation. 

 His process consists essentially in causing the mercury fulminate de- 

 tonator to act on pulverulent picric acid. The detonation of this 

 last brings about the detonation of the fused explosive. 



We have seen that the strong adhesion of the charge of explosive 

 to the walls of the projectile is an essential condition to security in 

 firing. From this standpoint melinite is above all most satisfactory. 

 It is estimated that more than 20 kilograms per square centimeter of 

 effort is necessary to effect the separation of a mass of melinite from 

 the metallic walls to which it has been fused. This adhesion appears 

 to increase markedly for some days after fusion. It is always 

 greater than the cohesion of the explosive. 



The fusing of the explosive in order to run it into the projectile 

 is generally effected in a water bath which is a thermosiphon. 

 Since melinite increases in volume at the moment of solidification, 

 experience shows that, as a consequence, cavities may be formed in 

 the interior of the charge of the projectiles. Practice has supplied 

 suggestions by which this serious defect may be overcome. An 

 essential precaution consists in preventing the presence of the melin- 

 ite in the thread of the nose fuse. Its presence on the outside of 

 the fuse or in its threads may cause a premature explosion. " 



Picric acid is obtained by nitrating phenol. To obtain a uniform 

 product, the crystalline phenol should fuse at 39° C. This sub- 

 stance is obtained in the distillation, between 150° and 200° C, 

 .of gas tar. It can be obtained synthetically through the oxidation 

 of benzene, the series of operations being as follows: The benzene 

 is treated at first with concentrated sulphuric acid. IMilk of lime 

 is added in excess to neutralize the acid. The solution is then 

 treated with sodium carbonate to form the sodium-benzene-sulpho- 

 nate (NaSOaCoHJ. This is evaporated to a sirup with addition of 



