Heat tracing definition

If you trace the word resin back far enough, you ll find that it was originally defined as a low molecular weight, natural polymer that is an exudate of (it exudes from) vegetable or non-vegetable matter. Examples are rosin (from pine trees), shellac (from insects), and both frankincense and myrrh (aromatic gums from an East African and an Asian species of tree). Resins like these do not flow if heat and pressure are applied, like plastics do. They decompose or melt. (This definition of resin is obsolete in commerce today.)... 

The flame is not, however, a discontinuity. There are definite gradients of temperature and composition because of conduction of heat and diffusion of reaction products into the fresh gas. The temperature gradients have been studied by three techniques direct measurement with very fine thermocouples (24, 25, 43) refraction of a narrow slit of light (11, 16) and tracing the path of a stroboscopically lighted dust particle and computing temperature from its direction and velocity (l, 27). 

Assay Preparation Transfer about 4 g of sample, accurately weighed, into a 250-mL Erlenmeyer flask, and add 80 mL of 0.5 N potassium hydroxide and 0.5 mL of phenolphtha-lein TS. Connect an air condenser at least 65 cm long to the flask, and heat the mixture on a hot plate for about 2.5 h. Remove the air condenser and add approximately 10% phosphoric acid to the hot mixture until it is definitely acid to Congo red test paper. Reconnect the air condenser, and heat until the fatty acids are liquified and clear. Cool, and transfer the mixture into a 250-mL separator with the aid of small portions of water and hexane. Extract the liberated fatty acids with three successive 25-mL portions of hexane, and collect the extracts in a second separator. Wash the combined hexane extracts with two 25-mL portions of water, and add the washings to the separator containing the water layer. Retain the combined hexane extracts for the determination of total fatty acids. Transfer the contents of the first separator to a 250-mL beaker, heat on a steam bath to remove traces of hexane, filter through acid-washed, fine-texture filter paper into a 500-mL volumetric flask, and finally dilute to volume with water (Solution I). Pipet 25.0 mL of this solution into a 100-mL volumetric flask, and dilute to volume with water (Solution II). Retain the rest of Solution I for the determination of Glycerin (below). 

Fig. 5.11 DSC trace (at 20 °C min ) of polymorph YN of 5-XII (see caption of Fig. 5.9 for definition of terms) showing an exothermic conversion (noted as C on the 5x expanded trace) and subsequent melting (noted as R, trace amount) and Y. The area under C gives an estimate of the enthalpy difference between YN and Y. (From Yu et al. 2000, with permission.) The authors attribute the differences between these traces and that in Fig. 5.10 to the difference in heating rate.

Experiment 52. — Dissolve a small piece of sodium hydroxide in an evaporating dish half full of water. Slowly add dilute hydrochloric acid, until a drop taken from the dish by means of a glass rod reddens blue litmus paper. Then evaporate to dryness by heating over a piece of wire gauze. Since the residue mechanically holds traces of the excess of hydrochloric acid added, it is necessary to remove this acid before applying any test. Heat the dish until all the yellow color disappears, then moisten the residue carefully with a few drops of warm water and heat again to remove the last traces of acid. This precaution is essential to the success of the experiment. Test a portion of the residue with litmus paper to find whether it has acid, basic, or neutral properties. Taste a little. Test (a) a solution of the residue for a chloride, and (b) a portion of the solid residue for sodium. Draw a definite conclusion from the total evidence. 

Since the vapour pressure increases rapidly with temperature, it is essential in accurate measurements to use a definite and constant temperature, and as it is affected by impurities it is equally necessary to employ highly purified liquids. Neglect of the second requirernent is probably the main source of error in older measurements, since traces of volatile substances (air, benzene) produce appreciable errors, In an unequally heated space, the vapour pressure generally corresponds with that at the lowest temperature Watfs principle ). This is the principle of Wollaston s 12 cryophorus (Greek kqvos, frost, I carry). 

Definite traces of heat-coagulable protein frequently are excreted, notably during the time of maximum nitrogen excretion (C21). 

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