Precautions, commercial solutions

The polarisation and cathode efficiency terms in equation 12.12 cannot be altered in practice to improve thickness distribution, as they tend to be decided by overriding considerations. It is usual to accept the distribution obtained without special precautions as being the best commercial solution, although the average thickness needed to achieve the necessary minimum... 

Handling, Storage, and Precautions solution of the reagent decomposes in air, should be stored and handled under inert atmosphere. Reacts vigorously with water and aqueous solutions. Due to strong dehydrating ability, spills may cause serious damage to skin and eyes. Commercial solution in THF is a flammable liquid. 

Three important precautions are needed when working with pipets and volumetric flasks. First, the volume delivered by a pipet or contained by a volumetric flask assumes that the glassware is clean. Dirt and grease on the inner glass surface prevents liquids from draining evenly, leaving droplets of the liquid on the container s walls. For a pipet this means that the delivered volume is less than the calibrated volume, whereas drops of liquid above the calibration mark mean that a volumetric flask contains more than its calibrated volume. Commercially available cleaning solutions can be used to clean pipets and volumetric flasks. 

Aluminium can be deposited from complex organic solutions if sufficient precautions are taken, and such coatings are now being produced commercially in North America. Two of the systems on record are (1) aluminium trichloride and lithium aluminium hydride dissolved in diethyl ether used at 40°C and 50A/m, and (2) aluminium chloride, n-butylamine and diethyl ether used at 20°C and 970 A/m. Deposits of 0-010 mm can be obtained on mild steel or copper at 20°C and 970 A/m using aluminium-wire anodes and nitrogen or argon atmospheres. 

Acetyl peroxide may readily be prepared and used in ethereal solution. It is essential to prevent separation of the crystalline peroxide even in traces, since, when dry, it is shock-sensitive and a high explosion risk [1], Crystalline material, separated and dried deliberately, detonated violently [2], The commercial material, supplied as a 30% solution in dimethyl phthalate, is free of the tendency to crystallise and is relatively safe. It is, however, a powerful oxidant [1]. Precautions necessary for the preparation and thermolysis of the peroxide have been detailed [3,4],... 

A boron analog - sodium borohydride - was prepared by reaction of sodium hydride with trimethyl borate [84 or with sodium fluoroborate and hydrogen [55], and gives, on treatment with boron trifluoride or aluminum chloride, borane (diborane) [86. Borane is a strong Lewis acid and forms complexes with many Lewis bases. Some of them, such as complexes with dimethyl sulfide, trimethyl amine and others, are sufficiently stable to have been made commercially available. Some others should be handled with precautions. A spontaneous explosion of a molar solution of borane in tetrahydrofuran stored at less than 15° out of direct sunlight has been reported [87]. 

In common with all other sensitive detection systems, maintenance of the label enzyme in its active state is important. The precautions detailed in Notes 1—3 should be observed to maximize the sensitivity achieved. Reagents for enhanced chemiluminescence can be prepared in the laboratory or ure available commercially (see Note 4). The purity of the substrate solution is important in achieving maximum sensitivity. Therefore, the precautions detailed in Notes 5-7 should be followed if preparing substrate solutions. The free base form of lummoi undergoes rearrangement ro a mixture of luminol and a series of contaminants. Therefore, luminol should be purified by recrystaliistation as the sodium salt before use (see Note 8). 

CAUTION Hydrazine is a suspected carcinogen and therefore should be handled with appropriate precautions. Hydrazine hydrate containing 60 per cent w/w and 98-100 per cent w/w NH2 NH2H20 is available commercially (1). A hydrazine solution, 60 per cent w/w of hydrazine hydrate, may be concentrated as follows. A mixture of 150 g (144 ml) of the solution and 230 ml of xylene is distilled from a 500-ml round-bottomed flask through a well-lagged Hempel (or other efficient fractionating) column in an atmosphere of nitrogen. All the xylene passes over with about 85 ml of water. Upon distillation of the residue, about 50 g of 90-95 per cent hydrazine hydrate (2) are obtained. 

For most commercial purposes these impurities are not harmful. By careful crystallization of the salt from solution, a product sufficiently free from these impurities can be obtained to be used as table salt. To obtain chemically pure sodium chloride, however, more elaborate precautions must be taken. A satisfactory method depends upon the insolubility of sodium chloride in a concentrated solution of hydrochloric acid. A nearly saturated solution of the rock salt is prepared, and, without removing the dirt and insoluble matter, enough pure sodium carbonate is added to precipitate the calcium and magnesium in the solution as carbonates. Into the clear filtrate gaseous hydrochloric acid is then passed until the greater part of the sodium chloride is precipitated, while the small amounts of sulphates and of potassium salts remain in the solution. The precipitate is drained and washed with a solution of hydrochloric acid until the liquid clinging to the crystals is entirely free from sulphates. 

Whereas carbonyl chloride itself is very moisture sensitive and requires the corresponding precautions such as efficiently dried glassware and solvents, the Box derivative is very stable and can be analysed by high performance liquid chromatography (HPLC) with ultra violet (UV) detection at 270 nm. Quantification is achieved by the standard addition procedure spiking carbonyl chloride into the test polymer solution. However, since Box is a commercially available chemical, it is advisable to work also with Box standards, especially when the method is used for the first time and when problems are experienced in the HPLC determination or the derivation procedure. The standards of the carbonyl chloride derivative are particularly useful to establish the analytical system and to check linearity of detector response as well as for the recovery check. 

Precaution. —HythvJiHoric acid gas is a corrosive poiso i. An aqueojis solution of the gas — commercial hydrojliioric acid—burns tJie flesh frightfully. 

Anhydrous diethyl ether, freshly obtained from a commercial supplier, is preferred for the reactions involving lithium hydro-aluminaie. The ether must be peroxide-free. Carbon dioxide must be rigorously excluded from these reaction systems. Explosions have been observed during evaporation of solutions of aluminum hydride and related compounds when carbon dioxide is present as an impurity.If it is necessary to concentrate ether solutions of lithium hydroaluminate by distillation, the following precautions must be observed. A large fluid volume must be maintained in the distillation flask such solutions should never be concentrated so far that very little ether remains in the reaction flask. Distillations must be effected in a protective atmosphere. Cyclic ethers, and especially tetrahydropyran solutions of lithium hydroaluminate, present a far greater explosion risk than diethyl ether solutions. 

Although heavy metal glazes are prohibited in commercial manufacture of ceramics in many countries, there are still reports of lead and other toxic heavy metals showing up in dishes imported from countries without similar controls or in ceramic items made by individuals who do not take the appropriate precautions. Because the glaze seems permanent and impervious to water and ordinary foods, it might seem that such materials would not be a hazard, but acidic solutions can extract significant amounts of the heavy metals and result in chronic low-level lead poisoning. 

When the appropriate precautions are taken the method appears particularly suited for measuring very low tensions 10 mN m sometimes even as low as 10 mN m ). Such ultralow tensions are for example encountered in micro-emulsion systems and in just phase-separated polymeric or micellar solutions. For phase-separated colloid-polymer systems de Hoog and Lekkerkerker ) even reported values down to a few pN m , reproducibly being obtained after implementing a number of methodical improvements. (Alternatives for low tensions are the sessile and pending (micro-) drop but these do not usually go below 10 mN m ) Commercial apparatus are nowadays available. A variant proposed by Than et al. J employs a thin rod in the axis of the cylinder, to reduce spin-up time and suppress drift. Another variant, proposed by Kokov, analyses the centrifugal field required to squeeze liquid out of an orifice" ). 

Commercial synthetic methanol (bp 65°) is 99+ per cent pure and contains only 0 to 0.5 per cent water and 0.02 to 0.10 per cent acetone. It does not form an azeotrope with water and therefore may be recovered from aqueous solutions in pure form by distillation. The small residual amount of water is best removed by treatment with magnesium methoxide. In a 2-1 flask fitted with a reflux condenser and a drying tube is placed 5 g of magnesium, 0.5 g of iodine, and 50 ml of methanol. The mixture is warmed on a steam bath until the iodine color disappears and a vigorous evolution of hydrogen occurs. If this does not occur, another 0.5 g of iodine is added and the mixture is again heated. After the methoxide has been formed, 1 1 of methanol is added, and the mixture is heated to reflux for 30 min. The alcohol is then distilled, with precautions taken to prevent entry of moisture. 

Carbon disulfide (bp 46°) is used as the solvent in many Friedel-Crafts reactions. It must be used with caution because of its very low flash point, which permits it to ignite on contact with heated surfaces. It should be distilled in such a manner that the vapors do not escape from the apparatus, and heat should be supplied by a steam bath and precautions taken to prevent overheating. The commercial material contains some odoriferous sulfur compounds which may be removed by successive treatment with mercury, mercuric chloride solution, and permanganate solution, and then washing with water, drying over phosphorus pentoxide, and distilling. ... 

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