Degree of purity

The required degree of purity varies with the application but the requirements in this domain are sometimes very important. Several tests are employed in the petroleum industry. 

Composition is normally expressed by a distillation curve, and can be supplemented by compositional analyses such as those for aromatics content. Some physical properties such as density or vapor pressure are often added. The degree of purity is indicated by color or other appropriate test (copper strip corrosion, for example). 

Traces of aldehyde are produced. If ether of a high degree of purity is required, it should l>e further shaken with 0-5 per cent, potassium permanganate solution (to convert the aldehyde into acid), then with i> per cent, sodium hydroxide solution, and finally with water. 

Absolute ethyl alcohol. Ethyl alcohol of a high degree of purity is frequently required in preparative organic chemistry. For some purposes alcohol of ca. 99 -5 per cent, purity is satisfactory this grade may be purchased (the absolute alcohol of commerce), or it may be conveniently prepared by the dehydration of rectified spirit with quicklime. Rectified spirit is the constant boiling point mixture which ethyl alcohol forms with water, and usually contains 95 6 per cent, of alcohol by weight. Wherever the term rectified spirit is used in this book, approximately 95 per cent, ethyl alcohol is to be understood. 

Acetone. The analytical reagent grade contains about 1 per cent, of water and meets most requirements. Synthetic acetone of a high degree of purity (water content about 1 per cent.) is also available as a technical product. 

The iodobenzene is conveniently distilled under reduced pressure and the fraction b.p. 77- 80°/20 mm. or 63-64°/8 mm. collected. The product has a higher degree of purity than that obtained directly from benzene (Section IV,21). 

Refined metals, as traded on the open market, vary considerably in composition. However, there are strict specifications for certain impurity elements for a number of metals. The degree of purity of common industrial metals obtained from modem metallurgical practices is shown in Table 2 (3). 

Polymer-grade terephthahc acid is over 99.9 wt % pure, exclusive of some residual water which has a specification. With this degree of purity. ... 

Feedwater The feedwater for a steam cycle must be purified. The degree of purity depends on the pressure of the boiler. Higher pressure boilers require higher feedwater purity. There is some trade-off between feedwater purity and boiler blowdown rate. However, increasing blowdown rate to compensate for lower feedwater purity is expensive, because blowdown water has been heated to the saturation temperature. Typical feedwater specifications for utihty boilers are given in Table 4. To some extent turbine steam purity requirements determine the feedwater purity requirements. The boiler-water siUca required to maintain adequate steam purity for higher pressure steam turbines is considerably less than the boiler could tolerate if deposition in the boiler were the only issue. 

Lower Oxides. A number of hard, refractory suboxides have been prepared either as by-products of elemental boron production (1) or by the reaction of boron and boric acid at high temperatures and pressures (39). It appears that the various oxides represented as B O, B O, B22O2, and B23O2 may all be the same material ia varying degrees of purity. A representative crystalline substance was determined to be rhombohedral boron suboxide, B12O2, usually mixed with traces of boron or B2O3 (39). A study has been made of the mechanical properties of this material, which exhibits a hardness... 

R wPrior to World War II, CN was produced mainly from cotton linters because of their higher degree of purity (alpha cellulose >98%). The high purity linters allowed a higher yield and better quaUty product compared to those obtained from less pure wood pulps or other cellulose sources. The development of highly purified chemical-grade wood pulps has allowed this material to be used in the same manner as are linters. 

Food Applications. A number of features make en2ymes ideal catalysts for the food industry. They are all natural, efficient, and specific work under mild conditions have a high degree of purity and are available as standardi2ed preparations. Because en2ymatic reactions can be conducted at moderate temperatures and pH values, simple equipment can be used, and only few by-products are formed. Furthermore, en2ymatic reactions are easily controUed and can be stopped when the desired degree of conversion is reached. 

Some materials are so reactive that they cannot be zone-melted to a high degree of purity in a container. Floating-zone techniques in which the molten zone is held in place by its own surface tension have been developed by Keck et al. [Phys. Rev., 89, 1297 (1953)]. 

Factors to be considered in maldng the selection of chromatography processing steps are cost, sample volume, protein concentration and sample viscosity, degree of purity of protein product, presence of nucleic acids, pyrogens, and proteolytic enzymes. Ease with which different types of adsorbents can be washed free from adsorbed contaminants and denatured proteins must also be considered. 

Irrespective of the grade of material to be purified, it is essential that some criteria exist for assessing the degree of purity of the final product. The more common of these include ... 

Air Quality (in context of the national parks ) the properties and degree of purity of air to which people and natural and heritage resources are exposed. 

Aluminum alloys can be divided into three classes aluminum of various degrees of purity wrought alloys and casting alloys. 

When the limonene to be identified is of high optical rotation, that is, of a high degree of purity in one of its optical forms, the tetrabromide is easy to identify but in the presence of much dipentene, it is necessary to recrystallise the compound repeatedly before a pure limonene tetrabromide is obtained. 

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