Woods metal bath

A. Wood s metal bath or a mixture (m. p. about 150°) of ten parts of potassium nitrate and seven and one-half parts of sodium nitrite may be used. 

In a 1-1. round-bottomed flask, fitted with a heated reflux condenser maintained at 100-110° (Note 1), are placed 44 g. of stearic acid (Note 2) and 20 g. (0.5 mole) of magnesium oxide (Note 3). The flask is immersed in a Wood s metal bath heated at 335-340° (Note 4). After the reaction has proceeded for 1 hour, 10-g. portions of melted stearic are added down the condenser at 15-minute intervals until an additional 240 g. (284 g., 1 mole total) has been added (Note 5). The heating is continued until the total reaction time is 10 hours. 

C. 3-Methylcoumarone. Dry 3-methylcoumarilic acid (50 g.) is distilled from a 250-ml. Claisen flask fitted with a long air condenser and immersed in a Wood s metal bath heated slowly to 280°. Carbon dioxide is evolved, and a cloudy liquid distils at 190-220°. The crude product is purified by redistillation through a Vigreux column (Note 6). The dear colorless distillate, weighing 31.5-33 g. (84-88%), boils at 195-197°, n 1.5520. 

Hydrogenated cottonseed oil, Coto Flakes, obtainable from the Procter and Gamble Company, Cincinnati, Ohio, is suitable for the bath. A Wood s metal bath may also be used. 

The benzene solution of the diazo compound is poured into a separatory funnel protected with a drying tube and connected to a 125-cc. Claisen distilling flask provided with a condenser set for downward distillation and arranged so that it can be heated in a bath of Wood s metal. The temperature of the metal bath being maintained at 100-110°, the benzene solution is dropped slowly into the hot flask. Under these conditions, the benzene is removed by distillation, and the diazo compound transformed into diphenylketene. The residue is distilled in vacuo in an atmosphere of nitrogen, and the fraction boiling at 115-125° at 3-4 mm. (Note 5) is collected. The yield is 31 g. (64 per cent of the theoretical amount) of a product which, on redistillation, yields 28 g. of diphenylketene boiling at 119-121° at 3.5 mm. (58 per cent of the theoretical amount). 

On somewhat smaller runs it may he more convenient to effect heating by the use of a wax or Wood s metal bath or an electric mantle. A hath or mantle temperature of 200° is sufficient for optimum 3neld. The reaction may froth vigorously if heated too rapidly or if the fumaramide is impure. 

Thermal sensitivity Temperature of ignition of FOX-7 is 215 °C as against 220 °C for RDX (Wood s metal bath). Further, excellent thermal stability is indicated by vacuum stability test for both FOX-7 as well as RDX. 

A Wood s metal bath is constructed as follows a solid mild steel block 30 cm long,... 

The test is performed with 20 mg of a sample, ground and dried. When the temperature of the bath is 300 °C, a test tube with the sample is immersed in the Wood s metal bath and a stopwatch is switched on simultaneously. When explosion of the sample occurs, the time is recorded by the stopwatch, that is, the time interval between the moment of insertion and the moment of explosion is noted. This period is the explosion delay (J D) or induction period at that temperature. In order to eliminate accidental variations, the mean of three readings is taken in all cases. The bath temperature may be decided depending upon the value of f D, that is, if value of ED is too high, the bath temperature may be increased whereas if it is too low, bath temperature may be decreased in order to improve the accuracy of the determination. 

A Beckman thermometer is used to read the temperature of the bath. When the temperature of the Wood s metal bath is -300 °C, a test tube with a sample is immersed in it. A stopwatch is used to record the time interval between the moment of immersion of sample in the bath and the moment of its explosion. If the explosion delay (ED) is more than 10/5 seconds, the temperature of the bath is increased by 10 °C and the experiment is repeated with a fresh sample. This exercise is repeated with incremental temperature changes (higher or lower) until an exact ED of 10-/5- seconds is obtained. This method is similar to that described by Weber in the literature [24]. 

Activation Energy It is experimentally seen that the explosion delay (ED) for the build-up of an explosion decreases with an increase in temperature. Therefore, energy of activation (IQ can be calculated on the basis of a relationship between the experimentally obtained ED and the absolute temperature of the Wood s metal bath. This relationship is expressed by an Arrhenius type of equation, that is, (Equation 3.3) ... 

T = absolute temperature of the Wood s metal bath A = frequency factor depending on the explosive. 

Another method is to place an expl sample directly on the molten Wood s metal bath or other metal sur-face heated at a controlled temp. The temp of the metal surface is increased until a vulue of 0.1 sec for ignition or explosion is estimated by the observer as an almost instantaneous interval of time(Refa 9 10 St... 

In a dry 200-cc. flask fitted with a ground-in reflux condenser and protected from moisture with a calcium chloride tube are placed 66 g. (0.32 mole) of a-bromonaphthalene (Note 1), 35 g. (0.39 mole) of dry powdered cuprous cyanide (Note 2), and 30 cc. of pyridine (Note 3) in the order mentioned. This mixture is heated in a Wood s metal bath (Note 4) at 215-225° for fifteen hours. The resulting dark brown solution is poured while still hot (about ioo°) into a flask containing 150 cc. of aqueous ammonia (sp. gr. 0.90) and 150 cc. of water. About 140 cc. of benzene is added, and the flask is stoppered and shaken until all the lumps have disintegrated. After the mixture has cooled to room temperature, 100 cc. of ether is added and the mixture filtered (Note 5). The filtrate is transferred to a i-l. separatory funnel and the aqueous layer separated (Note 6). The ether-benzene layer is washed successively with (a) four 100-cc. portions of dilute aqueous ammonia (Note 7), (b) two 100-cc. portions of 6 N hydrochloric acid (Note 8), (c) two 100-cc. portions of water, and (d) two 100-cc. portions of saturated sodium chloride solution. The ether and benzene are removed by distillation from a water bath, and the residue is distilled under reduced pressure from a 125-cc. modified Claisen flask. The temperature rises rapidly, and the yield of colorless a-naphthonitrile, b.p. i73-i74°/27 mm. (i66-i69°/i8 mm.) is 40-44 g. (82-90 per cent of the theoretical amount) (Notes 9 tnd 10). 

Henkin McGill (Ref 15) give the following expl times for 25 mg of Tetryl in copper shells of 0.635mm diam submerged into a hot Wood s metal bath ... 

High temperatures may be obtained also with the aid of baths of fusible metal alloys, e.g. Woods metal - 4 parts of Bi, 2 parts of Pb, 1 part of Sn and 1 part of Cu - melts at 71 °C Rose s metal - 2 of Bi, 1 of Pb and 1 of Sn - has a melting point of 94 °C a eutectic mixture of lead and tin, composed of 37 parts of Pb and 63 parts of Sn, melts at 183 °C. Metal baths should not be used at temperatures much in excess of 350 °C owing to the rapid oxidation of the alloy. They have the advantage that they do not smoke or catch fire they are, however, solid at ordinary temperature and are usually too expensive for general use. It must be remembered that flasks or thermometers immersed in the molten metal must be removed before the metal is allowed to solidify. 

A 0.5-g sample (a 0.01-g sample in the case of-> Initiating Explosives) is placed in a test tube and immersed in a liquid metal (preferably Wood s metal) bath at 100 °C (212°F), and the temperature is raised at the rate of 20 °C per minute until deflagration or decomposition takes place. 

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