Picric acid drop test

Place a mixture of 0-5 g. of finely powdered thiourea, 0-5 g. of the alkyl halide and 5 ml. of alcohol in a test-tube or small flask equipped with a reflux condenser. Reflux the mixture for a j)eriod depending upon the nature of the halide primary alkyl bromides and iodides, 10-20 minutes (according to the molecular weight) secondary alkyl bromides or iodides, 2-3 hours alkyl chlorides, 3-5 hours polymethy lene dibromides or di-iodides, 20-50 minutes. Then add 0 5 g. of picric acid, boil until a clear solution is obtained, and cool. If no precipitate is obtained, add a few drops of water. RecrystaUise the resulting S-alkyl-iso-thiuronium picrate from alcohol. 

More recently, explosives have been tested for impact sensitivity by an impact machine in which 40 mg of explosive on sandpaper are placed between an anvil and a steel cylinder. A 2.5 kg weight is dropped from different heights and the sound produced serves to indicate a go or no go . The result from 25 drops is calculated to give a height at which the probability of explosion is 50%. Results from a compilation104 are presented in Table 12 and show that the relative values of TNT and picric acid are reversed from the previous table. TNT is relatively more sensitive on the Type 12 impact machine than in the FI impact test. TATB is so insensitive that it fails to explode at the maximum drop height of the machine. 

Pentryl is less sensitive to impact than tetryl (according to Clark, the maximum height causing no explosion in the drop test is 50 cm for pentryl, whereas for tetryl it is 27.5 cm and for picric acid 42.5 cm). 

Trinitrophenetol or ethyl picrate, m.p. 78°, is prepared by the same methods as trinitroanisol. The explosive properties of the two substances have been studied by Desparmets and Calinaud, and by Desvergnes,72 who has reported the results of the earlier workers together with data of his own and discussions of methods of manufacture and of the explosive properties of mixtures with picric acid, ammonium nitrate, etc. Drop test with a 5-kilogram weight were as follows ... 

TNA shows about the same sensitivity as tetryl in the drop test. Lead block experiments have been reported which showed that 10 grams of TNA produced a net expansion of 430 cc., TNT 254 cc., picric acid 297 cc., tetryl 375 cc., guncotton 290 cc., and 75 per cent dynamite 300 cc.76 Experiments with the manometric bomb gave the results indicated below. 

Aranaz98 reports that the explosion of tetryl produces a temperature of 3339°. Tetryl is slightly more sensitive than picric acid, and considerably more sensitive than TNT, in the drop test. Experimenting with a 5-kilogram weight, Koehler found that a drop of 150 cm. caused the detonation of tetryl 10 times out of 10 trials, a drop of 100 cm. 9 times out of 10, of 50 cm. 5 times out of 10, and of 40 cm. 3 times out of 10. Martin99 has determined the minimum charges of various primary explosives necessary for the detonation of TNT and tetryl. The explosives were loaded into detonator capsules, and the initiators were compressed upon them at a pressure of 1100 kilos per square centimeter. 

GelatiAe.—5 grams of the powdered chocolate are treated with 50 c.c. of boiling water, 5 c.c. of 10% lead acetate solution being then added and the liquid filtered. The filtrate is tested with a few drops of saturated aqueous picric acid solution in presence of gelatine, a yellow precipitate forms. 

Tests (1) Picric Acid.— Add 5 drops of saturated picric acid solution to 5 ml. urine. Make alkaline with a few drops of 20 per cent. NaOH. A deep orange colour develops proportional to the amount of creatinine present. 

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