Melt bottle test

The simplest approach to investigate the potential of melt crystallization is the so-called bottle test. The feed mixture (molten or has to be molten) is filled in a glass bottle or flask. Thereafter, the flask is cooled slowly in a temperature-controlled bath or is allowed to cool at ambient conditions or, if necessary, in a freezer. Only a part not all has to be solidified Quite often, already a color shift clearly indicates a separation. However, to determine the quality of the purification, for instance by distribution coefficient, the residual melt has to be separated from the crystallized portion by decanting. Finally, the solid, the residual melt, and the feed material can be analyzed to decide whether melt crystallization is suitable as purification technique or not. The advantage of the bottle test is that it is quite simple. Only lab equipment is required to obtain the desired answer concerning the feasibility of melt crystallization. In case the result is positive, everything is clear. If the result, however, is not positive, a more detailed examination technique is required, for example, the cold finger experiment. 

A further simple, but very efficient and powerful technique to obtain important information especially on the purification by melt crystallization is the so-called cold finger experiment. Compared to the bottle test, more but simple lab equipment is required for this setup. Figure 15.7 shows the essential parts of a cold finger apparatus allowing a static operating mode. 

Preparation of Benzoyl Peroxide.1—Hydrogen peroxide (50 c.c. of about 10 per cent aqueous solution) kept well cooled in ice and continually shaken (preferably in a glass-stoppered bottle) is treated alternately with 4 A-sodium hydroxide solution and benzoyl chloride, added each a few drops at a time the solution is maintained faintly alkaline throughout. After about 30 c.c. of alkali and 15 g. of benzoyl chloride have been used up, the hydrogen peroxide has been decomposed and the benzoyl peroxide has separated in crystalline flocks, while the odour of the chloride has almost completely disappeared. The peroxide is filtered with suction, washed with water, and dried. Yield 10-12 g. Crystallised from a little alcohol, with which it should be boiled for a short time only, the substance forms beautiful colourless prisms. Melting point 106°-108° decomp. Heat a small quantity rapidly in a dry test tube over a naked flame. An especially pure product is obtained when a 1 von Pechmann and Vanino, Ber., 1894, 27, 1510. 

I) Solidification Point - 120.5° to 122°, and the substance shall melt to a bright, clear liquid free from scum and deposit. Test shall be conducted in an apparatus and in the manner similar to proced (1) described under Centralite 1, Analytical Procedures, except that no water is placed in the outer bottle, just air... 

Crude ethylidinebisacetoacetic ester as prepared in Preparation 74 is melted on the water bath and poured into 500 c.cs. 20% sulphuric acid in a round-bottomed flask attached to a reflux condenser. A few pieces of porcelain chips are added, and the whole vigorously boiled for 7 hours. It is then steam distilled until the distillate measures about 100 c.cs. The distillate is then set aside in a well-stoppered bottle. The residue is again refluxed for 7 hours and again steam distilled, 100 c.cs. of distillate being again collected. The process is repeated a third time, and then steam is blown into the mixture until no oil, or only a trace, separates from a test portion when treated with solid caustic potash. To the three united... 

If the test substance melts at a temperature lower than that specified for the determination, preheat the bottle and its contents for 1 to 2 h at a temperature 5° to 10° below the melting range, then continue drying at the specified temperature for the determination. When drying the sample in a desiccator, ensure that the desiccant is kept fully effective by replacing it frequently. 

Meanwhile melt some paraffine and when the bottle is warm enough not to be cracked by the hot paraffine, pour out the water and pour in the paraffine slowly until it about fills the neck of the bottle. As it cools, press it around the tubes and where the glass and paraffine meet. When cold, pour water into the bottle to detect any leak. If the apparatus is not tight, add more paraffine. It.may be necessary to adjust the position of the platinum strips when the test tubes, C and D, are lowered into the bottle. The electrolysis is accomplished the same as in Exp. 38. A is nearly filled with water containing 10 per cent of sulphuric acid, C 3.r)d D are filled with the same solution and clamped over the platinum strips as shown in Fig. 42. When one tube is full of gas, the current is stopped, the volume measured as in Exp. 38, and each gas is tested with a lighted taper or blazing stick of wood. 

LDPE containers are used to collect shallow snow samples or to store them after melting. LDPE represents a compromise between chemical resistance during strong cleaning treatments, low content of impurities and a low price (see Table 3.3). In any case, before use, all the plastic bottles and items must be extensively cleaned following tested procedures (10, 27). 

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