Glass vessels

This is a disproportionation reaction, and is strongly catalysed by light and by a wide variety of materials, including many metals (for example copper and iron) especially if these materials have a large surface area. Some of these can induce explosive decomposition. Pure hydrogen peroxide can be kept in glass vessels in the dark, or in stone jars or in vessels made of pure aluminium with a smooth surface. 

The second danger may arise from the careless treatment of the hydride in a glass vessel with water or acid a significant volume of hydrogen may be evolved, and a fragment of the hydride may ignite and so cause an explosion. These conditions should never arise in the course of careful work. 

Adventitious losses of the reagent, due, e.g., to the chemical action of the alkaline glass vessels, slight absorption by the corks, etc., are almost identical for the actual and the control experiments and therefore do nor affect the difference in result between the two experiments. 

The use of sodium fluoborate solution supersedes the less convenient flueborlc acid and permits the preparation to be carried out in ordinary glass vessels. 

Manufacture. Fluoroborate salts are prepared commercially by several different combinations of boric acid and 70% hydrofluoric acid with oxides, hydroxides, carbonates, bicarbonates, fluorides, and bifluorides. Fluoroborate salts are substantially less corrosive than fluoroboric acid but the possible presence of HF or free fluorides cannot be overlooked. Glass vessels and equipment should not be used. 

Methyl bromide is nonflammable over a wide range of concentrations in air at atmospheric pressure and offers practically no fire hazard. With an intense source of ignition, flame propagation within a narrow range from 13.5 to 14.5% by volume has been reported. The material has no flash point. Thermal decomposition in a glass vessel begins somewhat above 400°C. 

Hydrofluoric acid [7664-39-3] M 20.0, b 112.2"(aq azeotrope, 38.2% HF), d 1.15 (47-53% HF), pK 3.21. Freed from lead (Pb ca 0.002ppm) by co-precipitation with Srp2, by addition of lOmL of 10% SrCl2 soln per kilogram of the cone acid. After the ppte has settled, the supernatant is decanted through a filter in a hard-rubber or paraffin lined-glass vessel [Rosenqvist Am J Sci 240 358 1942. Pure aqueous HF solutions (up to 25M) can be prepared by isothermal distn in polyethylene, polypropylene or platinum apparatus [Kwestroo and Visser Analyst 90 297 7965]. HIGHLY TOXIC. 

Closed or open test eells. Open test eells are eonneeted to a seeond eontainment vessel. Test eells of various materials ean be used ineluding stainless steel, Hastelloy C276, and glass. Glass test eells of various sizes and shape are suitable for testing fine ehemieal and pharmaeeutieal produets/reaetion eonditions when the proeess is only in glass vessels or when only small samples are available, or if the samples are very expensive. 

Hasegawa and Sato analyzed motion pictures and radiation measurements at a distance of 15 m from the center of the glass vessel. They then correlated, first, fireball duration and maximum diameter to initial fuel mass and, second, radiation to initial vapor pressure. 

It consists of a porous cell which foims the cathode chamber and contains 20 grams nitrobenzene and 160 grains 2 5 per cent, caustic soda solution. The two aie kept well mixed throughout the operation by a rapidly revolving stinei. The cathode is a cylinder of nickel gauze (12 cms. x S 5 cms. = too sq. cms.). The anode chamber is the outer glass vessel or beaker. 

HF, CH3CN. In certain sensitive substrates it may be advisable to run this reaction in a polypropylene vessel, as was the case in Schreiber s synthesis of FK-506, where the yield increased from 35% to 73% after switching from the standard glass vessel. This is presumably because of the products formed when HF reacts with glass. 

GlMschen, n. little glass, small glass vessel or tube. 

Massglas, n. measuring glass, marked glass vessel. 

Caution This reaction should he carried out in an explosion-proof room behind a safety shield because it involves a glass vessel under pressure. 

The capacity of a glass vessel varies with the temperature, and it is therefore necessary to define the temperature at which its capacity is intended to be correct in the UK a temperature of 20 °C has been adopted. A subsidiary standard temperature of 27 °C is accepted by the British Standards Institution, for use in tropical climates where the ambient temperature is consistently above 20 °C. The US Bureau of Standards, Washington, in compliance with the view held by some chemists that 25 °C more nearly approximates to the average laboratory temperature in the United States, will calibrate glass volumetric apparatus marked either 20 °C or 25 °C. 

Sometimes a film of the sulphide adheres to the glass vessel in which precipitation was carried out this can be dissolved in a little ammonia solution and the sulphide re-precipitated with the acid washing liquor. 

One form of calomel electrode is shown in Fig. 15.1(a). It consists of a stoppered glass vessel provided with a bent side tube fitted with a three-way tap which carries a short upper and a long lower tube the latter is drawn out to a constriction at the bottom end. A short platinum wire is fused into the bottom of the vessel so that it protrudes into the interior, and a narrow glass tube sealed to the bottom of the vessel is bent round parallel to the vessel. A little mercury placed in the bottom of this tube provides electrical connection with the interior of the vessel through the sealed-in platinum wire. Mercury and mercury compounds must be handled with care (see Section 16.8). 

A bolometer is essentially a thin blackened platinum strip in an evacuated glass vessel with a window transparent to the infrared rays it is connected as one arm of a Wheatstone bridge, and any radiation absorbed raises the temperature of the strip and changes its resistance. Two identical elements are usually placed in the opposite arms of a bridge one of the elements is in the path of the infrared beam and the other compensates for variations in ambient temperature. Both the above receptors give a very small direct current, which may be amplified by special methods to drive a recorder. 

In flame spectrophotometric measurements we are concerned with solutions having very small concentrations of the element to be determined. It follows that the standard solutions which will be required for the analyses must also contain very small concentrations of the relevant elements, and it is rarely practicable to prepare the standard solutions by weighing out directly the required reference substance. The usual practice therefore is to prepare stock solutions which contain about 1000 ig mL 1 of the required element, and then the working standard solutions are prepared by suitable dilution of the stock solutions. Solutions which contain less than 10 igmL 1 are often found to deteriorate on standing owing to adsorption of the solute on to the walls of glass vessels. Consequently, standard solutions in which the solute concentration is of this order should not be stored for more than 1 to 2 days. 

Phenylphenylsulfanyl)benzenesulfonyl chloride (10 g, 28 mmol) and CuCI (27 mg, 0.28 mmol) were mixed together in a glass vessel under an N2 atmosphere. The contents were stirred and the vessel was... 

DIVER METHOD- This is a modification of the hydrometer method. Variation in effective density i and hence concn, is measured by totally immersed divers. These are small glass vessels of approximately streamline shape, ballasted to be in stable equilibrium, with the axis vertical, and to have a known density slightly greater than that of the sedimentation liq. As the particles settle, the diver moves downwards in hydrodynamic equilibrium at the appropriate density level. The diver indicates the position of a weight concn equal to the density difference between the diver and the sedimentation liq. Several divers of various densities are required, since each gives only one point on the size distribution curve... 

Zollinger, 1981). In the presence of less than 5 ppb of 02 it obeys first-order kinetics in glass vessels, but zero-order kinetics in Teflon vessels. With between 60 and 100 ppb of 02, a fast initial reaction slackens off after about 15% conversion autocatalysis is observed on exposure to air, but in 100% 02 there is again a first-order reaction. 

Shortly after the 94 was precipitated, a considerable amount of K.2SiF6 was observed to separate, as a result of the fact that precipitation had been performed in glass vessels. This will be avoidable in future work because we have now developed suitable fluoride-resistant micro vessels.)... 

Bozzetto (Bergamo, Italy) offers a continuous chlorosulfonic acid sulfona-tion process which comprises two water-jacketed glass vessels for sulfonation and neutralization, and an HC1 absorption column. Organic feedstock and chlorosulfonic acid are mixed on a rotating disk. Under the centrifugal action of the disk, the reaction mixture is sprayed as a thin film onto the wall of the reaction vessel. The acid product falls to the base of the reactor and then onto a similar rotating disk system, where it is mixed with alkali and sprayed onto the wall of the neutralization vessel. The unit is operated under slightly reduced pressure to remove HC1 gas. 

Fig. 17. Bipolar capillary cell (a) 125 fim gaps, (b) glass vessel, (o) electrical leads, (d) stack of graphite plates, (e) solution flow. (Taken from Beck and Guthke, 1969.)...

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