Aluminium block

The hquid is constantly mixed by the shearing action of the gas stream which reduces the hkehhood of sample boil-over in the heated aluminium block. 

If the analysis is to be carried out in a similar way to total N in herbage, by acid-digestion in test tubes in an aluminium block followed by a colorimetric autoanaiysis procedure, then take a 0.5-g sample of air-dry soil. If serious frothing occurs, take 0.2 g soil, and adjust the calculation accordingly. Reducing the amount to 0.1 g may give peaks which are too small to be read with confidence. See Chapter 7 (pp. 138-141) for details of standards, reagents and method. 

Acid digestion unit - see Chapter 4 for details of aluminium blocks and hotplate. 

Fig, 3.2-1. Experimental build-up a) glass tube b) boreholes with slip ring seals c) aluminium block NS 60 d) glass head e) inert gas bridge f) ampoule with a standard solution... 

Urine (5 ml) urine spiked with 0.2% (v/v) isopropylamine is placed in a screw-capped 15-ml vial [28]. Pelleted potassium hydroxide (3 g) is added before sealing the vial with an airtight polytetrafluoroethylene-lined septum cap. Potassium hydroxide raises the pH of the sample to ensure that the amines are present as volatile bases. The vial is heated in an aluminium block at 90 C for 20 min. While still in this block, 2 ml head-space gas is withdrawn through the septum with a disposable syringe and injected immediately on the gas chromatography column. The operating temperatures of the column, injector port and detector unit are 70 C isothermal, 150 C and 200 C, respectively, with nitrogen carrier gas at 60 ml/min. This allows quantification of TMA and other amines. TMA N-oxide is measured after quantitative reduction into TMA. For this, titanous chloride (30%, w/v 0.2 ml) is added to 2 ml urine in a screw-capped vial and incubated for 30 min at room temperature. The sample is then diluted ten-fold with distilled water and analysed as described above. The result represents the sum of TMA and TMA N-oxide present in the sample. 

Fig. 1. Shallow aluminium block-bath for heating many test-tubes.

Fig. 2. Top surface of deep aluminium block-bath for evaporation to dryness in test-tubes.

It is always indispensable for almost all self-heating chemicals, irrespective of whether they are of the TD type or of the AC type, to determine the or the T, of each run by inserting the reference cell assembly into the adiabatic jacket in the adiabatic self-heating process recorder, or into the aluminium block bath in the isothermal storage testing device, prior to the insertion of the sample cell... 

The cross section of the device is shown in Fig. 119. The aluminium block bath measures 107 mm by 107 mm and 79.6 mm in height. The glass closed cell measures 1.4 cm in outside diameter and about 3 cm in length in other words, it... 

Figure 119. The cross section of the isothermal storage testing device, a. To a temperature recorder b. Thermocouple c. Aluminium lid d. Aluminium block bath e. Glass closed cell f. Sample g. Heater.

Preheating of the aluminium block bath of the isothermal storage testing device and the choice of a nominal T, in the isothermal storage test performed for 0.4 g of collodion cotton confined in the closed cell... 

Insertion of the reference cell assembly into the preheated aluminium block bath in the isothermal storage testing device and the determination of the exact value of TV of the run... 

The reference cell assembly is raised with a pair of fairly large pincers and is inserted carefully down to the bottom of the hole, 23 mm in diameter, 75 mm in depth, bored vertically at the center of the upper surface of the preheated aluminium block bath which is set in the isothermal storage testing device in the meantime, the temperature of the bath is maintained at the T, K of the run throughout every run. 

The exact value of T, of the run is then determined as the arithmetic mean of a series of digital outputs of T, recorded for 2 d prior to the insertion of the sample cell assembly into the aluminium block bath. Fluctuations of the values of T, during this time are within 0.05 K. 

The test, including the heating of the aluminium block bath, is interrupted automatically as soon as the temperature of collodion cotton in the cell increases by 0.3 K (by 0.2 K, as to nitroglycerin) from the T, in order to prevent the cell from exploding. As a matter of fact, however, the test is usually interrupted as soon as the temperature of the high explosive in the cell increases obviously in excess of the T,. ... 

The temperature of the aluminium block bath is set at a proper value, i.e., the nominal T, of the run, by means of the ten-key on the block bath on the basis of the self-healing property of the powdery chemical of the quasi-AC type tested to give estimated values of At of 1 7 d in the isothermal storage test. It is usually a temperature 0" 15 K. lower than the endothermic peak temperature, which is measured by thermal analysis, such as DTA or DSC, of each chemical in the case of powdery chemicals of the quasi-AC type tested herein, with the result that the 7) ranged from 30.08 t for AMVN to 94.0 C for ABCN. As to LPO, the T, ranged from 48.55 to 53.0 C. 

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