Cleaning practices General

Where a heterocyclic organometallic reagent is required, Grignard and zinc derivatives are often satisfactory complications sometimes attend the use of lithio derivatives. The use of boronic acids has become very popular on account of their clean reactions, general stability to air and water, and their compatibility with practically any functional group furan, thiophene, indole and pyridine boronic acids have all been used. " ... 

Recrystallisation. The process of purification by recrystallisation is undoubtedly the most frequent operation in practical organic chemistry, and it is one which, when cleanly and efficiently performed, should give great pleasure to the chemist, particularly if the original crude material is in a very impure and filthy condition. Yet no operation is carried out so badly, wastefully (and thoughtlessly) by students in general, not only by elementary students, but often by research students of several years experience. The student who intends later to do advanced work must master the process, for unless he can choose a suitable solvent and then successfully recrystallise often minute quantities of material, he will frequently find his work completely arrested. 

Fig. 28.6. Fatigue data for welded joints in clean air. The class given to a weld depends critically on the weld detail and the loading direction. Classes B and C must be free from cracks and must be ground flush with the surface to remove stress concentrations. These conditions ore rarely met in practice, and most welds used in general construction hove comparatively poor fatigue properties.

The hazards of chemicals are commonly detected in the workplace first, because exposure levels there are higher than in the general environment. In addition, the exposed population is well known, which allows early detection of the association between deleterious health effects and the exposure. The toxic effects of some chemicals, such as mercury compounds and soot, have been known already for centuries. Already at the end of the eighteenth century, small boys who were employed to climb up the inside of chimneys to clean them suffered from a cancer of the scrotum due to exposure to soot. This was the first occupational cancer ever identified. In the viscose industry, exposure to carbon disulfide was already known to cause psychoses among exposed workers during the nineteenth century. As late as the 1970s, vinyl chloride was found to induce angiosarcoma of the liver, a tumor that was practically unknown in ocher instances. ... 

Dilution of fumes in these areas is generally required for one of two reasons either to reduce the level of harmful (toxic or irritant) fumes to a safe level, normally below the OES (Occupational Exposure Standard) or to dilute offensive odors. Care must be taken with the latter to ensure that the problem is not merely passed on to neighbors. If it is, then a local extract with air-cleaning equipment will be preferred if it is practical. Indeed, a local extract system is always preferable, since it removes the problem at source, resulting in a cleaner environment within the building. 

Although many standards exist for cleaning treatments for metal surfaces, for example Defence Standard DEF STAN 03-2/1, these are often fairly general guides which in some cases may be regarded as somewhat outdated due to recent advances in treatment technology and changes in industrial practice. 

Most fish is still caught at sea and must be cooled soon after it is taken on board, and kept cold until it can be sold, frozen or otherwise processed [45]. The general practice is to put the fish into refrigerated sea water tanks, kept down to 0°C by direct expansion coils or a remote shell-and-tube evaporator. The sea water must be clean and maybe chlorine dosed. At this condition, fish can be kept for up to four days. 

In addition to supplying the various water-steamside conditioning equipment, chemical treatments, and periodic cleaning or other specialist services, service companies are expected to provide advice, practical expertise, and general support for their program in a proactive manner, to prevent waterside and operational problems from occurring. 

The precise protocols necessary to achieve effective corrosion control will vary dependent on individual boiler design and operation. For example, control of alkalinity is fundamental in controlling corrosion mechanisms. In small to midsize, general-purpose and industrial boilers, it is common practice to obtain adequate BW alkalinity as part of any water treatment program that operates under a free-caustic regimen. This approach generally is perfectly acceptable, and such programs normally can be relied on to ensure a clean, scale- and corrosion-free boiler. 

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