Indicator methods

The indicator method is especially convenient when the pH of a weU-buffered colorless solution must be measured at room temperature with an accuracy no greater than 0.5 pH unit. Under optimum conditions an accuracy of 0.2 pH unit is obtainable. A Hst of representative acid—base indicators is given in Table 2 with the corresponding transformation ranges. A more complete listing, including the theory of the indicator color change and of the salt effect, is also available (1). 

J)Other analytical methods which include, among many, a thermometric method (104), a high frequency titration (105), and a colored indicator method (106). 

Solid-phase acidic dyes ai e also used in the study of the ternai y systems with pyrazolone derivatives. In addition, the colorless complex of the investigated metals with pyrazolone derivatives has been studied by means of the metal-indicator method. 

Cold alignment. There are two predominant techniques used for cold alignment. These are (1) the face-OD method, and (2) the reverse-dial indicator method. Both these techniques utilize dial indicators. For highspeed turbomachinery, the reverse-dial indicator method is the superior method and should be used. 

Figure 18-17. Graphic plotting for reverse-dial indicator method.

There are two primary methods of aligning machine trains dial indicator alignment and optical, or laser, alignment. This section provides an overview of each, with an emphasis on dial-indicator methods. 

Dial-indicator methods (i.e., reverse-dial indicator and the two variations of the rim-and-face method) use the same type of dial indicators and mounting equipment. However, the number of indicators and their orientations on the shaft are different. The optical technique does not use this device to make measurements, but uses laser transmitters and sensors. 

There are three methods of aligning machinery with dial indicators. These methods are (1) two-indicator method with readings taken at the stationary machine, (2) two-indicator method with readings taken at the machine to be shimmed, and (3) indicator reverse method. Methods 1 and 2 are often considered to be one method, which is referred to as rim-and-face. 

Although some manufacturers insist on the use of the reverse indicator method for alignment or, at least, as a final check of the alignment, two basic factors determine which method should be used. The determining factors in method selection are (1) end play and (2) distance versus radius. 

If the distance between the points of contact of the two dial indicators set up to take rim readings for the indicator reverse method is larger than one-half the diameter of travel of the dial indicator set up to take face readings for the two-indicator method, the indicator reverse method should be used. 

There are three primary methods of aligning machine trains with dial indicators reverse-dial indicator method, also called indicator-reverse method, and two variations of the rim-and-face method. 

There are advantages with the reverse-dial indicator method over the rim-and-face method - namely accuracy and the fact that the mechanic is forced to perform the procedure by the book, as opposed to being able to use trial and error . Accuracy is much better because only rim readings are used. This is because rim readings are not affected by shaft float or end play as are face readings. In addition, the accuracy is improved compared with rim-and-face methods because of the length of the span between indicators. 

Reverse-dial indicator method (also referred to as indicator-reverse method) is the most accurate form of mechanical alignment. This technique measures offset at two points and the amount of horizontal and vertical correction for offset and angularity is calculated. Rim readings are taken simultaneously at each of the four positions (12, 3, 6, and 9 o clock) for the movable machine (MTBS/MTBM) and the stationary machine. The... 

As with the reverse dial indicator method, the measuring device used for rim-and-face alignment is also a dial indicator. The fixture has two runout indicators mounted on a common arm as opposed to reverse-dial fixtures, which have two runout indicators mounted on two separate arms. 

Rim-and-face measurements are made in exactly the same manner as those of reverse-dial indicator methods. 

With horizontally mounted units, it is possible to correct both angularity and offset with one adjustment. In order to compute the adjustments needed to achieve the desired alignment, it is necessary to establish three horizontal measurements. These measurements are critical to the success of any alignment and must be accurate to within f inch (see Figure 54.20). Again, the procedure described here is for the reverse dial indicator method (see Figure 54.16). 

The following procedure can be used on vertical units to obtain angularity and offset values needed to compare with recommended manufacturer s (i.e., desired) tolerances in order to determine if a unit is out of alignment. Perform an alignment check on the unit using the reverse-dial indicator method. 

Either the Mohr titration or the adsorption indicator method may be used for the determination of chlorides in neutral solution by titration with standard 0.1M silver nitrate. If the solution is acid, neutralisation may be effected with chloride-free calcium carbonate, sodium tetraborate, or sodium hydrogencarbonate. Mineral acid may also be removed by neutralising most ofthe acid with ammonia solution and then adding an excess of ammonium acetate. Titration of the neutral solution, prepared with calcium carbonate, by the adsorption indicator method is rendered easier by the addition of 5 mL of 2 per cent dextrin solution this offsets the coagulating effect of the calcium ion. If the solution is basic, it may be neutralised with chloride-free nitric acid, using phenolphthalein as indicator. 

C. Potentiometric methods. This is a procedure which depends upon measurement of the e.m.f. between a reference electrode and an indicator (redox) electrode at suitable intervals during the titration, i.e. a potentiometric titration is carried out. The procedure is discussed fully in Chapter 15 let it suffice at this stage to point out that the procedure is applicable not only to those cases where suitable indicators are available, but also to those cases, e.g. coloured or very dilute solutions, where the indicator method is inapplicable, or of limited accuracy. 

The green colour due to the Cr3+ ions formed by the reduction of potassium dichromate makes it impossible to ascertain the end-point of a dichromate titration by simple visual inspection of the solution and so a redox indicator must be employed which gives a strong and unmistakable colour change this procedure has rendered obsolete the external indicator method which was formerly widely used. Suitable indicators for use with dichromate titrations include AT-phenylanthranilic acid (0.1 per cent solution in 0.005M NaOH) and sodium diphenylamine sulphonate (0.2 per cent aqueous solution) the latter must be used in presence of phosphoric) V) acid. 

Titrations can be carried out in cases in which the solubility relations are such that potentiometric or visual indicator methods are unsatisfactory for example, when the reaction product is markedly soluble (precipitation titration) or appreciably hydrolysed (acid-base titration). This is because the readings near the equivalence point have no special significance in amperometric titrations. Readings are recorded in regions where there is excess of titrant, or of reagent, at which points the solubility or hydrolysis is suppressed by the Mass Action effect the point of intersection of these lines gives the equivalence point. 

Blinks, J. R. (1989). Use of calcium-regulated photoproteins as intracellular Ca2+ indicators. Method. Enzymol. 172 164-203. 

Illarionov, B. A., et al. (2000). Recombinant obelin cloning and expression of cDNA, purification, and characterization as a calcium indicator. Method. Enzymol. 305 223-249. 

Data sets become two dimensional in any of the following situations (in order of decreasingly rigorous theoretical underpinnings) and are analyzed by the indicated methods. 

Konmova, Ts.B., Popov, M.S., and Venichenko, A.S. "Study of the Interaction of Zirconium with Certain Monocarboxylic Acids by the Metal Indicator Method," Russian Journal of Inorganic Chemistry. 1975, 20(6), 861 865. 

The precision for METHOD B is significantly larger than METHOD A, indicating METHOD A is more precise than METHOD B. 

Table 6.1 shows the results obtained by Sturgeon et al. [21] for a stored coastal water sample. The mean concentrations and standard deviations of replicates (after rejection of outliers on the basis of a simple c test-function) are given for each method of analysis. Each mean reflects the result of four or more separate determinations by the indicated method [21 ]. 

Plotting of the dependences Q(t) in log-log coordinates allows to determine the value Df according to the slope of these dependences in their linearity case. In figure 1 the mentioned dependences for process of PAA imidization without filler are shown. As can be seen, these dependences are linear, that allows to make estimation Df by the indicated method. 

Adsorption-coprecipitation phenomenon using fluorescein, dichlorofluorescein and tetrabromofluo-rescein (eosin) essentially impart the fluoresceinate ion that is absorbed on the AgCl particles. At the equivalence point, the AgCl particles change from white to pink due to the coprecipitation of silver fluoresceinate. In short, the adsorption indicator method is quite rapid and capable of providing very accurate results for the estimation of Cl with AgN03. 

A good number of amperometric titrations may be performed on considerably dilute solutions (say, 1(H M) at which neither potentiometric nor visual indicator methods ever can give precise and accurate results, and... 

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