SUBJECTS Dewar flask

The result of the above calculation suggests that the condition, UKK A, may hold for 400 cm each of average organic powdery chemicals of the TD type charged each in the 500 cm Dewar flask used in the BAM test and placed each in the atmosphere under isothermal conditions as well and therefore, the spatially uniform distribution of internal temperature may be effected in each of them in the early stages of the self-heating process, with the result that each of them may take the same values of qj and Tuq - Tset-up) as 400 cm of a liquid charged in the Dewar flask and placed in the atmosphere under isothermal conditions (For matters relevant to this subject, refer to Subsection 5.5.1). 

The glassy solutions were prepared by a rapid freezing at 77 °K. The transparent samples of the neutral ice were obtained from twice-distilled water subjected to a slow freezing at a temperature of 270° to 272°K. in special molds. The produced ice plates of about 5 mm. in thickness were irradiated in the sealed ampules at a temperature of 77 °K. After irradiation the ampules were opened and the samples were transferred into the Dewar flask for taking optical measurements. 

To a quartz cuvette fitted with a Teflon stopcock was added 53 mg 2,6-dichloro-benzoquinone and 63 mg phenyl m-xylyl acetylene in CH2CI2 in a 0.1 M solution of each substance under argon. The cuvette was then placed in a clear Dewar flask filled with water at 25°C and irradiated with focused light from a medium-pressure mercury lamp (500 W) passed through an aqueous IR filter and an ESCO 410 nm filter. This ensured that the quinone itself was excited and not the diarylacetylene. After 22 h, the solvent was evaporated, and the residue was subjected to flash chromatography. 1-(3,5-Dimethylphenyl)-l-benzoyl-1-methylene-3,5-dichlorocyclohexa-2,5-dien-4-one was obtained as the major product, which was further recrystallized from acetonitrile, m.p., 191-192°C. The minor product was identified only by GC/MS. The total yield of quinone methide was 88% based on 62% of conversion. 

Cryogenic liquids must be stored, shipped, and handled in containers that are designed for the pressures and temperatures to which they may be subjected. Materials that are pliable under normal conditions can become brittle at low temperatures. Dewar flasks, which are used for relatively small amounts of material, should have a dust cap over the outlet to prevent atmospheric moisture from condensing and plugging the neck of the tube. Special cylinders insulated and vacuum-jacketed with pressure-relief valves and rupture devices to protect the cylinder from pressure buildup are available in capacities of 100 to 200 liters (L). 

Dewar (vacuum) flasks also pose a hazard of implosion if they are subjected to mechanical shock. These containers should be securely wrapped with tape to prevent injury from flying glass. 

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