Hot-stage microscope

Differential scanning calorimetry Differential thermal analysis Hot stage microscope... 

The DTA or hot-stage microscope can be used under ignition conditions to obtain an ignition temperature. The nature of the decomposition can also be observed at a range of temperatures. Observations such as decomposition with evolution of gases prior to ignition are regarded as potentially hazardous. 

McCrone of ARF, consists of following the behavior of crysts of the compd on a hot stage microscope at temps close to the mp. The most stable samples of MEDINA were found to be those recrystd from et chloride/iso-Pr ale the least were prepd by vacuum evapn (Ref 11, p 30)... 

More recently the thermal decompn of single large ciysts of AP has been studied on a hot-stage microscope. It was found that the low temp decompn started on a cryst face as a dark spot which rapidly expanded into a hole which then spread thruout the cryst. The ciysts were not consumed, but a residue of finely powd AP was always left (Ref 45)... 

If the phases present can be unambiguously identified, microscopy can be used to determine the geometry of interface initiation and advance, and to provide information about particle sizes of components of mixed reactants in a powder. Problems of interpretation arise where materials are poorly crystallized and where crystallites are small, opaque, porous or form solid solutions. With the hot-stage microscope, the progress of reactions can be followed in some instances and the occurrence of sintering and/or melting detected. 

The melting point was taken on a Reichert hot stage microscope. This instrument is available from William J. Hacker and Company, Inc., P.O. Box 646, West Caldwell, New Jersey 07006. 

For this method, either a weighed amount of the solute (or a definite amount of the solvent) is placed in a suitable vessel. While agitating the system at constant temperature, known amounts of the solvent (or the solute) are added gradually until the solubility limit is reached. Appropriate checks must be carried out to ensure that the system is very close to equilibrium when the content or temperature of the system is recorded. In this method of temperature variation, attention is usually focused on the last small crystal. The equilibrium temperature is taken as the mean of the two temperatures at which the crystal either slowly grows or slowly dissolves. This procedure may also be carried out at the microscale by examining a small volume of the system under a hot-stage microscope. 

The melting range of the isotactic, crystalline sample is determined with the aid of a hot-stage microscope the following conditions of the sample can be distinguished ... 

The melting points, enthalpies, and associated entropies for a series of A -aryl-4//-benzo[ ][l,3]thiazin-2-amines 71 are presented in Table 3 <2004MI6291>. The melting points of the compounds determined by differential scanning calorimetry (DSC) agreed with the results obtained by hot-stage microscope. 

Although the azide could not be purified by recry stn because of its instability in warm so Ins, it could be purified by subliming a small sample at 150° on a hot stage microscope (Ref 3, p 35)... 

Characterization of the Copolymer. The SO- content in the copolymer was calculated from the sulfur content determined by the Schoniger method. The reduced viscosity of the copolymer was determined at 30 °C with an Ostwald viscometer. DMF containing 0.1% LiCl was used as solvent at 0.2 gram/100 ml. The melting point of the terpolymer was measured by a hot-stage microscope. 

For the sublimation of quantities of materials in the region of a few milligrams, the vacuum sublimation block supplied by Reichert-Jung is particularly suitable. This block is located on the hot-stage microscope (see p. 240), the sublimation chamber carefully evacuated, the temperature raised slowly, and the process of sublimation observed through the microscope. 

Preparation of N-(3-chloropropyl)-N -[2-(l,3-dioxanyl)-ethyl]-piperazine A solution of 30 g (0.15 mol) of N-[2-(l,3-dioxanyl)-ethyl]-piperazine and 11.8 g (0.075 mol) of l-bromo-3-chloropropane in 150 ml of dry benzene was refluxed with stirring for 5 hours. After cooling, the N-[2-(l,3-dioxanyl)-ethyl]-piperazinium bromide which had precipitated was filtered off, the filtrate was concentrated in vacuo and the residual oil was distilled. 14.1 g (68%yield) of N-(3-chloropropyl)-N -[2-l,3-dioxanyl)-ethyl]-piperazine which occurred as a light yellow oil were obtained. Boiling point 152°C to 155°C under 0.07 mm Hg (nD23 = 1.49 40). The disuccinate prepared in acetone and recrystallized from acetone melts at 104°C to 105°C on a hot stage microscope. 

Figure 12.8 Hot-stage microscope pictures of uncooked (at 30°C) and cooked (at 70°C) native and various chemically modified tapioca starches in water containing sucrose (20% by weight) and sodium chloride (5% by weight), indicating different ease of cooking as a result of food ingredients.

The systematic use of the hot stage microscope employing mainly the Kofler hot stage was originally described in the book by Kofler and Kofler (1954) (the founders... 

Fig. 4.1 An illustration from the original paper by Lehman (1877i>) on Physical Isomerism showing his hot stage microscope and various shapes of crystals observed. Another noteworthy feature of this figure is the time vs temperature cooling curve for ammonium nitrate in the upper left hand comer, showing four inflection points that indicate polymorphic transitions. (Reprinted by permission from Zeitschrift fur Kristallographie.)...

Fig. 4.3 (See also colour plate section.) An enantiotropic phase transformation in 2,4,6-trinitro-5-fert-butyl-ra-xylene as observed on the hot stage microscope. Form 11 is stable at room temperature and the thermodynamic transition point is at 84 °C. (a) Room temperature stable Form 11, the coarse crystals at upper right embedded in aggregate of Form 1. (b) On heating Form n grows at the expense of Form 1. (c) At 84 °C the transformation can be halted, (d) Above 84 °C Form 1 is stable and has grown at the expense of Form 11. (From Kuhnert-Brandstatter 1971, with permission.)...

Fig. 4.9 (See also color plate section.) Photographs of the microscope shde Kofler preparations showing the various phases of the benzocaine picric acid (BC PA) binary system. Top (a) the photomicrograph of the recrystalhzed contact preparation of BC and PA at 25 °C. The interference colours are due to the use of crossed polarizers. The pure compounds are at the extremities of the preparation, while in the region where the original compounds have merged a number of different areas may be observed, due to the formation of different crystalline species combining the two components. Heating this preparation on the hot stage microscope...

---