Cleaning of Vessels

While in analytical operations, since one generally deals with aqueous solutions, the cleaned vessels may be used even if wet, it frequently happens in organic work, in experimenting with liquids not miscible with water, that dry vessels must be employed. In order to dry small pieces of apparatus rapidly, they should be rinsed first with alcohol and then with ether. To remove the last portions of the easily volatile ether, air from a blast is blown through the vessel for a short time, or the ether vapours are removed by suction. The alcohol and ether used for rinsing can frequently be used again it is convenient to keep two separate bottles for the wash alcohol and wash ether, into which the substances, after being used, may be poured. 

For rapid drying of large vessels this method is costly. In this case the procedure is as follows The wet vessel is first drained as thoroughly as possible, and then heated with constant turning in a large luminous blast-flame, while, by means of a blast of air from bellows or other source, the water vapour is driven out. It 

Vessels may be cleaned in part by rinsing them out with water with the use of a feather or flask-cleaner. If the last portions of the solution of a solid, eg. in alcohol, are to be removed from a flask, it is not washed out at once with water, but first with a small quantity of the solvent, and then afterwards with water. If the vessel contained a liquid not miscible with water, it is first washed with alcohol and then with water., Resinous or tarry impurities adhering firmly to the walls can be removed by crude concentrated sulphuric acid. The action of this latter may be strengthened by adding a little water to it, by which heat is generated also by the addition of some crystals of potassium dichromate. At times the impurities adhere so firmly that the vessel must be allowed to stand in contact with sulphuric acid for a long time. Crude concentrated nitric acid, or a mixture of this with sulphuric acid, is also used at times for cleaning purposes. Impurities of an acid character can, under certain conditions, be removed by caustic soda or caustic potash. 

In a limited number of substances containing nitrogen, the presence of the latter may be proved by heating the substance with an excess of pulverised soda-lime in a test-tube with a Bunsen flame this causes decomposition with evolution of ammonia, which is detected by its odour or by means of a black colour imparted to a piece of filter-paper moistened with a solution of mercurous nitrate. Nitro-compounds, eg., do not give this reaction. 

Test for Sulphur. — The qualitative test for sulphur is made in the same manner as that for nitrogen. The substance is heated in a small tube with sodium. After the mass has cooled it is treated with water, and to one-half of the solution is added a small quantity (a few drops) of a solution of sodium nitroprus-siate, just prepared by shaking a few crystals with water at the ordinary temperature. A violet colouration indicates the presencq 

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Introducing mechanical cleaning of vessels (e.g. wall wipers) and pipes (e.g. pipeline pigging) that process viscous materials and require periodic cleaning with water. 

A red zone / area exists if the TGW value is exceeded or if the measures required by the surveillance authorities are not respected. In general, work under these conditions is not allowed. However, under certain circumstances or for certain activities (e.g. tunnel construction, cleaning of vessels and tanks, work to remove asbestos etc.) in which the TGW cannot be respected, exemptions are foreseen. 

Particular precautions were recommended to prevent contamination or losses during extraction, including careful cleaning of vessels. Evaporation to dryness has to be avoided (risks of degradation or volatilization). Recovery experiments have to be performed in order to ensure that no loss or transformation of the species occur during the extraction/clean-up process. 

In the Finnish printing ink plants, the combined solvent levels were still in the 1980 s often out of compliance when compared to the OELs. Significant airborne concentrations were observed for toluene, ethyl acetate (TLV 400 ppm, the Finnish OEL 300 ppm), aromatic solvent naphtha (the Finnish OEL 240 mg/m ), and acetone (TLV and the Finnish OEL 500 ppm). The cleaning of vessels of barrels was again an especially problematic task. If cleaning is done manually, it is difficult to control the exposure sufficiently well with local ventilation but respiratory protection is also needed. 

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