The Experimental Procedure

In this section, we will describe the experimental apparatus that is typically utilized in order to perform a heterodyne-detected OKE experiment. In particular we will present the experimental systems developed and assembled in our laboratory. 

First of all, a laser source able to produce short pulses with high energy is required. Presently there are a large variety of ultrafast laser systems available on the market. Substantially all these laser systems are based on the Ti sapphire solid state active medium and on the Kerr lens mode-locking principle. There is a large amount of literature on this subject [69] and we will recall here only the principal features of our present laser system. This is composed of a Kerr lens mode-locked Ti sapphire oscillator and a chirped pulse amplification system [19,70], see Fig. 2.2. The oscillator source is a Kerr-lens mode-locked Ti sapphire laser (FemtoRose lOMDC, by R D Ultrafast Laser) pumped by 

Though there is a most common optical scheme to perform HD-OKE experiments, a few variants are possible [71,72]. 

Here we describe our optical set-up that has shown to be particularly successful in order to induce and detect the birefringence dynamics with high energy and low repetition laser pulses [19,25,27-29,36,37]. In this experimental setup (see Fig. 2.3) the laser beam is divided into the exeitmg and the probing beam (about 80%-20%) by a beam splitter, BSl. The exeiting pulse arrives 

The detection of the signal in HD experiments is not always straightforward. In fact several contributions are simultaneously present on the detector, see next section, and the disentanglement of them is required. In our experiment we used a differential photodiodes system one photodiode measures all the electromagnetic fields coming from the sample, E - -, the other photodiode 

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It is not uncommon for this situation to apply, that is, for a Gibbs mono-layer to be in only slow equilibrium with bulk liquid—see, for example. Figs. 11-15 and 11-21. This situation also holds, of course, for spread monolayers of insoluble substances, discussed in Chapter IV. The experimental procedure is illustrated in Fig. Ill-19, which shows that a portion of the surface is bounded by bars or floats, an opposing pair of which can be moved in and out in an oscillatory manner. The concomitant change in surface tension is followed by means of a Wilhelmy slide. Thus for dilute aqueous solutions of a methylcellu-... 

The experimental procedure used by Hansen and co-workers involved the use of a loudspeaker magnet to drive a rod touching the surface (in an up-and-down motion) and... 

The selection of the operating principle and the design of the calorimeter depends upon the nature of the process to be studied and on the experimental procedures required. Flowever, the type of calorimeter necessary to study a particular process is not unique and can depend upon subjective factors such as teclmical restrictions, resources, traditions of the laboratory and the inclinations of the researcher. 

Unfortunately, in most cases not all the available information on a reaction is given in the reaction equation in a publication, and even less so in reaction databases. To obtain a fuller picture of the reaction that was performed, the text describing the experimental procedure in the publication or a lab journal) would have to be consulted. Reaction products that are considered as trivial, such as water, alcohol, ammonia, nitrogen, etc., are generally not included in the reaction equation or mentioned in the text describing the experimental work. This poses serious problems for the automatic identification of the reaction center. It is highly desirable to have the full stoichiometry of a reaction specified in the equation. 

Method 3 (F. Adickes, 1930). The experimental procedure is similar to that described in Method 2 except that excess of ethyl formate (b.p. 

The experimental procedure to be followed depends upon the products of hydrolysis. If the alcohol and aldehyde are both soluble in water, the reaction product is divided into two parts. One portion is used for the characterisation of the aldehyde by the preparation of a suitable derivative e.g., the 2 4-dinitrophenylhydrazone, semicarbazone or di-medone compound—see Sections 111,70 and 111,74). The other portion is employed for the preparation of a 3 5-dinitrobenzoate, etc. (see Section 111,27) it is advisable first to concentrate the alcohol by dis tillation or to attempt to salt out the alcohol by the addition of solid potassium carbonate. If one of the hydrolysis products is insoluble in the reaction mixture, it is separated and characterised. If both the aldehyde and the alcohol are insoluble, they are removed from the aqueous layer separation is generally most simply effected with sodium bisulphite solution (compare Section Ill,74),but fractional distillation may sometimes be employed. 

Alternatively a mixture of 90 g. of sodium benzenesulphonate and 60 g. (36 ml.) of phosphorus oxychloride may be used. The experimental procedure is identical with that for phosphorus pentachloride, but the yield is slightly better. 

Mercury porosimetry is generally regarded as the best method available for the routine determination of pore size in the macropore and upper mesopore range. The apparatus is relatively simple in principle (though not inexpensive) and the experimental procedure is less demanding than gas adsorption measurements, in either time or skill. Perhaps on account of the simplicity of the method there is some temptation to overlook the assumptions, often tacit, that are involved, and also the potential sources of error. 

What criteria were considered in designing the experimental procedure ... 

Following the movement of airborne pollutants requires a natural or artificial tracer (a species specific to the source of the airborne pollutants) that can be experimentally measured at sites distant from the source. Limitations placed on the tracer, therefore, governed the design of the experimental procedure. These limitations included cost, the need to detect small quantities of the tracer, and the absence of the tracer from other natural sources. In addition, aerosols are emitted from high-temperature combustion sources that produce an abundance of very reactive species. The tracer, therefore, had to be both thermally and chemically stable. On the basis of these criteria, rare earth isotopes, such as those of Nd, were selected as tracers. The choice of tracer, in turn, dictated the analytical method (thermal ionization mass spectrometry, or TIMS) for measuring the isotopic abundances of... 

Numerous examples of standard methods have been presented and discussed in the preceding six chapters. What we have yet to consider, however, is what constitutes a standard method. In this chapter we consider how a standard method is developed, including optimizing the experimental procedure, verifying that the method produces acceptable precision and accuracy in the hands of a single analyst, and validating the method for general use. 

All of the experimental procedures we have discussed in this chapter yield, among other things, information concerning the average molecular weight of a... 

The experimental procedures depend to a large extent on the use to which the explosive is to be put. Comparison is often made to proven explosives of known performance. Many of the most commonly used tests in the various categories of concern are as follows ... 

Thixotropy and Other Time Effects. In addition to the nonideal behavior described, many fluids exhibit time-dependent effects. Some fluids increase in viscosity (rheopexy) or decrease in viscosity (thixotropy) with time when sheared at a constant shear rate. These effects can occur in fluids with or without yield values. Rheopexy is a rare phenomenon, but thixotropic fluids are common. Examples of thixotropic materials are starch pastes, gelatin, mayoimaise, drilling muds, and latex paints. The thixotropic effect is shown in Figure 5, where the curves are for a specimen exposed first to increasing and then to decreasing shear rates. Because of the decrease in viscosity with time as weU as shear rate, the up-and-down flow curves do not superimpose. Instead, they form a hysteresis loop, often called a thixotropic loop. Because flow curves for thixotropic or rheopectic Hquids depend on the shear history of the sample, different curves for the same material can be obtained, depending on the experimental procedure. 

Two reactions of the non-aromatic 4,4-disubstituted pyrazolones are worthy of mention. Carpino discovered that 4,4-dihalogenopyrazolones (365) and 4-substituted 4-halogenopyrazolones (366) when treated with bases yield a, 8-alkynic and -alkenic acids, respectively (66JOC2867). The reaction proceeds through an oxopyrazolenine (2,3-diazacyc-lopentadienone (367) (B-74M140408). A modification of the experimental procedure transforms (365) into bimanes (368) (82JOC214), which are formed from (367 R = X),... 

Most of these compounds, for instance pyrazole itself, are today commercially available, so there is only a minor interest in detailing the experimental procedures used. The best way to prepare pyrazole is the Protopopova method (Section 4.04.3.3.2) and a modification using hydrazine hydrate instead of a hydrazine salt has recently been patented (80GEP2922591). 

The experimental procedure and method of treatment of compression-permeability data have been explained by Grace [Chem. Eng. Prog., 49, 303, 427 (1953)], who showed that the values of a measured in such a cell and in a pressure filter were the same, and by Tiller [Filtr Sep., 12, 386 (1975)]. 

Acknowledgment The authors wish to express their gratitude to Dr. J. Edwards of Syntex Research who provided the experimental procedure utilizing silver carbonate on Celite. We are also indebted to the Synthetic Chemical Research Department of Merck Sharp Dohme Research Laboratories for providing time to complete this review and also to Miss Joanna Mohr for her patience and care in preparing the manuscript. 

The next seven references are cited not because of the experimental procedures described but because they indicate diversification in the types of enamines prepared and studied. Both Paquette (25) and Kasper 26) have condensed 2,5-methylene-l,2,5,6-tetrahydrobenzaldehyde (5-nor-bornene-2-carboxyaldehyde) (2) with several cyclic and open-chain aliphatic secondary amines. Kasper studied the ratio of endo to exo aldehyde formed upon hydrolysis of these enamines and the dihydro enamines. Paquette investigated the addition of sulfene to the enamines. -Fluoro-... 

Another important synthetic method for the reduction of ketones and aldehydes to the corresponding methylene compounds is the Woljf-Kishner reduction. This reaction is carried out under basic conditions, and therefore can be applied for the reduction of acid-sensitive substrates it can thus be regarded as a complementary method. The experimental procedure for the Clemmensen reduction is simpler however for starting materials of high molecular weight the Wolff-Kishner reduction is more successful. 

The Diels-Alder reaction is the most important method for the construction of six-membered rings. For example it can be used as a step in a benzo-anellation procedure. The experimental procedure is simple, and yields are generally good side reactions play only a minor role. 

Nevertheless the Elbs reaction is a valuable method for the preparation of dihydroxy benzenes. The experimental procedure is simple, and the reaction conditions are mild a variety of functional groups is tolerated. 

Rearrangements and other side-reactions are rare. The ester pyrolysis is therefore of some synthetic value, and is used instead of the dehydration of the corresponding alcohol. The experimental procedure is simple, and yields are generally high. Numerous alkenes have been prepared by this route for the first time. For the preparation of higher alkenes (> Cio), the pyrolysis of the corresponding alcohol in the presence of acetic anhydride may be the preferable method." The pyrolysis of lactones 9 leads to unsaturated carboxylic acids 10 ... 

Treatment of aniline 1 with nitric acid in the presence of tetrafluoroboric acid leads to a relatively stable benzenediazonium tetrafluoroborate 2 by the usual diazotization mechanism. There are several variants for the experimental procedure. Subsequent thermal decomposition generates an aryl cation species 4, which reacts with fluoroborate anion to yield fluorobenzene 3 " ... 

Certain commercial equipment, instruments, or materials are identified in this report to specify adequately the experimental procedure. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose. 

The polymers studied and the experimental procedure were described in the last section. The samples were made of the same PC-TLCP composite and the pure TLCP Vectra A950, respectively. To study the influence of sample forms and geometries on mechanical constants, plate samples (80 x 80 x 2 mm-) were also injection molded with a film gate. Tensile samples were then cut from the plate in the longitudinal (//) and transverse... 

The experimental procedure consisted of casting the varnish on glass plates by means of a spreader bar having an 0-102 mm (0 004 in) gap this produced a wet film 0-051 mm (0-002 in) thick that yielded a dried film of 0-025 mm (0-001 in). This standard thickness was used throughout and resistances are quoted in cm. The cast films were dried for 48 h in a glove box followed by a further 48 h in an oven at 65°C. 

Calmagite. This indicator, l-(l-hydroxyl-4-methyl-2-phenylazo)-2-naphthol-4-sulphonic acid, has the same colour change as solochrome black, but the colour change is somewhat clearer and sharper. An important advantage is that aqueous solutions of the indicator are stable almost indefinitely. It may be substituted for solochrome black without change in the experimental procedures for the titration of calcium plus magnesium (see Sections 10.54 and 10.62). Calmagite functions as an acid-base indicator ... 

Full details are given for the determination of aluminium by this method. Many other metals may be determined by this same procedure, but in many cases complexometric titration offers a simpler method of determination. In cases where the oxine method offers advantages, the experimental procedure may be readily adapted from the details given for aluminium. 

Discussion. The turbidity of a dilute barium sulphate suspension is difficult to reproduce it is therefore essential to adhere rigidly to the experimental procedure detailed below. The velocity of the precipitation, as well as the concentration of the reactants, must be controlled by adding (after all the other components are present) pure solid barium chloride of definite grain size. The rate of solution of the barium chloride controls the velocity of the reaction. Sodium chloride and hydrochloric acid are added before the precipitation in order to inhibit the growth of microcrystals of barium sulphate the optimum pH is maintained and minimises the effect of variable amounts of other electrolytes present in the sample upon the size of the suspended barium sulphate particles. A glycerol-ethanol solution helps to stabilise the turbidity. The reaction vessel is shaken gently in order to obtain a uniform particle size each vessel should be shaken at the same rate and the same number of times. The unknown must be treated exactly like the standard solution. The interval between the time of precipitation and measurement must be kept constant. 

Oxabicyclo[4.1.0]hept-3-enes with a bromo substituent in position 2 can be converted to oxepins 11 by reaction with an appropriate base such as potassium ter+butoxide or triethylamine (see the experimental procedures for the preparation of the parent system in Houben-Weyl, Vol. 6/ld, pi78 and Vol. 6/4, p462).12,156,157 Usually the reaction products are mixtures of oxepin 11 and benzene oxide 12. In the case of ZerZ-butyl 7-oxabicyclo[4,1.0]hept-3-ene-2-carboxylate, the equilibrium lies completely on the benzene oxide side 12a.158... 

The most common direct methods are the oven, the distillation, and the Fischer methods. They can be made precise by careful standardization of the experimental procedures their accuracy can be assured only by calibration against some accurate reference method. 

Di-2-propenyltin dibromide, available from 2-propenyl bromide and tin powder, reacts with aldehydes in the presence of monosodium (+)-diethyl 2,3-dihydroxybutanedioate to give ho-moallylic alcohols in good yields with 42-71% ee the experimental procedure is relatively straightforward98. 

Other examples of esterification with trialkyloxonium salts have been reported.7,8 The present procedure offers the advantages that the reactive carboxylate ion is generated in sitv and that a low-boiling, nonaqueous solvent is employed, whereby the experimental procedure is considerably simplified. A related method has been reported which utilizes a hindered amine wdth dimethyl sulfate [Sulfuric acid, dimethyl csterj as the alkylating agent.9 The present procedure is carried out under somewhat milder conditions and avoids the use of highly toxic reagents. 

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