Reducing, volumetric determination

Instead of making a direct volumetric determination of the hydrosulphite it is possible to modify the process by estimating volumetrically the product of a primary reaction. For example the hydrosulphite solution may be submitted to atmospheric oxidation and the resulting acidity determined with standard alkali,2 or a mercuric salt may be reduced, the mercury produced being estimated subsequently by the addition of standard iodine solution and titration of the excess of iodine one molecule of hydrosulphite is equivalent to an atom of mercury and therefore to two atoms of iodine.4 Similarly, instead of the gravimetric estimation of silver as described above, the latter may be redissolved in nitric acid and determined volumetrically.5... 

Two separate portions of 50 c.c. of the filtrate are placed in 100 c.c. flasks, one being made up to volume with distilled water and the other inverted in the ordinary way, neutralised and made up to volume both solutions are then polarised and the saccharose calculated by Clerget s formula. The results may be checked by volumetric determinations with Fehling s solution, the saccharose and the pre-existing reducing sugars being then calculated. 

Aqueous solutions of osmium tetroxide are readily reduced by the introduction of practically any metal except those known as the precious metals.3 Thus zinc, silver, mercury, etc., effect the precipitation of metallic osmium from acidulated solutions in a very pure form. In the last-named ease an amalgam is produced from which the osmium is obtained by distilling off the mercury. Ferrous sulphate and stannous chloride4 also reduce the tetroxide solutions, but hydrogen,5 sulphur and selenium 6 appear to have no action under ordinary conditions. Sulphur dioxide reduces the solution to osmium sulphite, whilst potassium iodide reduces it to dioxide with liberation of iodine—a reaction that may be utilised in the volumetric determination of osmium.7... 

Reduction of Ferric Salts.—The reverse reactions, namely conversion of ferric salts into ferrous, are likewise easily effected by means of the usual reducing agents, such as nascent hydrogen, sulphur dioxide, etc. By the introduction of zinc into an acidified solution of a ferric salt, reduction is rapidly caused. Excess of acid slightly retards the reaction.4 This affords a convenient method of volumetrically determining the presence of ferric iron, the solution after reduction being titrated with permanganate. 

Volumetric determination may be made by reducing the titanium to the trivalent condition with zinc and then titrating with potassium permanganate, ferric chloride, or methylene blue.5... 

Total lung deposition estimates were determined by Heyder et al. (1975) for nose and mouth breathers at various tidal volumes of air (Table 27.5). Their deposition estimates for nose breathers at tidal volumes of 250 and 500 cm demonstrate reasonable agreement with probabilistic deposition estimates for adult nose breathers the results are within a factor of 2. At increased tidal volumes of 1000 and 1500cm, however, their results do not compare well with this assessment s probabilistic estimates. This occurs due to the significantly reduced volumetric flow rates of air that they used, as compared to those employed by our theoretical estimates. As volumetric flow rate is increased, a reduction in particle deposition occurs in the lung region, due to the decreased residence time in the respiratory tract. 

Hydrogen chemisorption Static H2 chemisorption at 100°C on the reduced cobalt catalysts was used to determine the number of reduced surface cobalt metal atoms. This is related to the overall activity of the catalysts during CO hydrogenation. Gas volumetric chemisorption at 100°C was performed using the method described by Reuel and Bartholomew [6]. The experiment was performed in a Micromeritics ASAP 2010 using ASAP 2010C V3.00 software. 

Iron was present as Fe " in the calcined precursors. For all the catalysts the reduction procedure described in Sec. 2.1 resulted in incomplete reduction of the Fe to metallic iron. This is in agreement with the findings of previous authors [6,11]. The individual percentage reductions of Fe to Fe°, as determined by the separate gravimetric and volumetric measurements (Sec. 2.2), are shown in Table 1. The values are calculated on the assumption that all the Fe is reduced to Fe prior to the onset of reduction to Fe°. There is good agreement between the two methods. Table 1 also records the actual Fe/(Fe + Mg) ratio in the catalysts as determined by atomic absorption spectroscopy (AAS) on the calcined precursors. 

At low temperatures, the nonenzymatic reaction is reduced to a larger extent than the enzymatic reaction. The mass transfer rate is reduced to a smaller extent. Mass transfer limitation is required for high enantiomeric excess and determines the conversion rate. Therefore, the volumetric productivity decreases at lower temperatures. The equilibrium constant is considerably higher at low temperatures, resulting in a higher extent of conversion or a lower HCN requirement. Both the volumetric productivity and the required enzyme concentration increase by increasing the reaction temperature and aqueous-phase volume while meeting the required conversion and enantiomeric excess [44]. The influence of the reaction medium (solvent and water activity) is much more difficult to rationalize and predict [45],... 

Determination of the relation between sodium chloride and silver.—Ten samples of a known weight of purified silver were dissolved in nitric acid, and each was treated with purified sodium chloride. The excess of silver was determined volumetrically and the precipitated silver chloride was reduced to metallic silver and weighed. The best representative value of these determinations was 54 2078 parts of NaCl were required for 100 parts of silver. 

The detection and determination ot the perchlorates.—The perchlorates give no precipitates with silver nitrate or barium chloride soln. cone. soln. give a white crystalline precipitate with potassium chloride. Unlike all the other oxy-acids of chlorine, a soln. of indigo is not decolorized by perchloric acid, even after the addition of hydrochloric acid and they do not give the explosive chlorine dioxide when warmed with sulphuric acid unlike the chlorates, the perchlorates are not reduced by the copper-zinc couple, or sulphur dioxide. Perchloric acid can be titrated with —iV-alkali, using phenolphthalein as indicator. The perchlorates can be converted into chlorides by heat and the chlorides determined volumetrically or gravimetrically they can be reduced to chloride by titanous sulphate 28 and titration of the excess of titanous sulphate with standard permanganate they can be fused with zinc chloride and the amount of chlorine liberated can be measured in terms of the iodine set free from a soln. of potassium iodide and they can be... 

Instead of being determined volumetrically, however, the ammonium or quinoline molybdophosphates are usually reduced to another molybdenum complex, molybdenum blue (heteropoly blue), which is then analysed spectrophotometrically (see Section II.B.2.C). 

Volumetric Estimation.—Tellurium may be determined by oxidation from the tellurous to the telluric condition, using an excess of potassium dichromatc or permanganate and subsequently titrating the excess of oxidising agent with a standard solution of a suitable reducing agent.2 In order to obtain accurate results with the potassium dichromate titration, certain very definite steps in the procedure are essential, and it is necessary to control the course of the reaction, since hydrochloric and telluric acids interact with production of chlorine. 

The crystal structure of Pd. h Y zeolite was determined before and after hydrogen reduction at different temperatures. When the zeolite is evacuated at 600°C, Pd2+ ions are mainly found to occupy SI sites within the sodalite cages. Hydrogen adsorption at 25° C results in a complete withdrawal of Pd2+from SI sites. This displacement out of cation sites is attributed to the reduction Pd2+ — Pd(0) consistent with hydrogen volumetric measurements. Reduced palladium remains atomically dispersed inside the sodalite cages up to about 200° C. Between 200 and 800° C, Pd 0) atoms migrate toward the outer surface of the zeolite where they agglomerate into 20-A diameter crystallites. 

The determination of the reducing sugars may be either volumetric or gravimetric. 

More rapidly, and in most cases with sufficient accuracy, the invert sugar may be determined by the volumetric method as described in the general methods, but the influence of the large excess of saccharose on the reducing power is then neglected. 

In addition to maltose, beer confabs small proportions of other reducing substances, which are however usually calculated as maltose. The gas-free beer is suitably diluted (dilution of 25 c.c. to 100 c.c. generally suffices) and the reducmg substances determined by means of Fehling s solution, either gravimetrically or volumetrically ... 

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