Wood’s 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. 

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 ... 

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. 

A solution of 2,6-diamino-5-benzamidopyrimidin-4-ol (4.9 g, 20 mmol) in 2 M NaOH (10 mL) was evaporated to dryness on a steam bath under reduced pressure. The sodium salt thus obtained was heated at 280 °C for 1.5 h in a Wood s metal bath. Water evolved and the solid turned dark. After cooling, the residue was dissolved in HjO (400 mL) containing 2 M NaOH (10 mL). The alkaline solution was filtered and acidified with HOAc. The precipitate was filtered, washed with H,0 and dried at 100 C yield 2.4 g (53%). 

This test bridges the gap in the growth from thermal decomposition reaction to explosion and eventually involves fast oxidation reactions. A small sample of explosive is pressed into a blasting cap cup made of gilding metal. The cup is then inserted into a molten Wood s Metal bath. The time it takes from insertion in the bath until some noticeable reaction takes place (usually a mild explosion) is noted. The test is repeated at several different bath temperatures. See Table 6.3. A smooth curve is drawn through the data points (time to explosion versus bath temperature), and the temperatures that cause reaction in 1, 5, and 10 s are interpolated from the graph. 

For temperatures above the useful range of the oil and wax baths (approximately 160°), a sand bath or a Wood s metal bath is commonly used. A sand bath is simply a metal dish (usually in the form of a hemisphere) containing sand. The flask is immersed in the sand, and the bath is heated with a bunsen burner. The sand serves to make the heating more uniform than would be possible with a flame and to minimize temperature fluctuations because of its fairly larg e heat capacity. 

A Wood s metal bath contains a metal alloy (50 per cent bismuth, 25 per cent lead, 12.5 per cent tin, and 12.5 per cent cadmium) with a low melting point ( 70°) which may be used up to quite high temperatures ( 400°). The metal is easily oxidized at the higher temperatures and, therefore, is usually covered with a protective layer of carbon. An electrically heated bath is recommended, since the temperature is then easily controlled. This may be made by taking an ordinary tin can (preferably low and wide), covering it with asbestos paper, and winding a coil of nichrome wire around it. The wire is covered with more asbestos paper held in place by some coils of copper wire. The entire assembly is placed inside a metal container such as... 

A nitrogen inlet is constructed using a fine capillary held through a screw-top Quickfit thermometer adapter, placed on top of the glass tube. The system is adjusted such that the capillary reaches the bottom of the glass tube. The side-arm is connected to a gas bubbler. The glass tube is then placed in a Wood s metal bath, which is heated by means of a Bunsen burner (care ). 

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