Chemical Tests and Determinations

The examination of meat concerns in the first place the food inspector, whose duty it is to determine that the meat is good for food and has not been obtained from diseased animals. The analyst s task is usually to determine the nutritive value of the meat by estimating its principal components and to test for the presence of preservatives or colouring matters. The more common chemical tests and determinations are as follows ... 

The examination of black pigments comprises certain technical and physical tests, indicated in paragraphs 1-3, and also chemical tests and determinations (paragraphs 4-7) for the purpose either of distinguishing the different products from one another (especially the determination and examination of the ash) or of ascertaining their purity and value. 

Chemical Tests and Determinations, 753 Chewing Gum Base, 782 Bound Styrene, 782 Molecular Weight, 783 Quinones, 784 Residual Styrene, 784 Total Unsaturation, 785 Chicle, 249... 

The special pigments of Centrospermae have attracted considerable interest during the past 40 years the pigment composition of red beet has especially been the topic of many investigations. Initially the betalains of red beet were separated and isolated using paper electrophoresis (244) and column chromatography (216) their chemical structure was elucidated by means of chemical tests and spectroscopic methods (214). The traditional methods for the quantitative determination of betacyanins and betaxanthins in beet root were spectrophotometry, mainly the Nilsson method (216). More recently, HPLC has become the method of choice for the separation and quantification of beet pigments (247). 

The technical tests required for cinnabar and vermilion are more particularly those of the quality and intensity of the colour, the covering power, fineness, stability towards light and behaviour towards other pigments (white lead, zinc white) these are carried out by the general methods already indicated. The chemical analysis comprises principally the tests and determinations here described. 

The chemical tests include Determination of the moisture and ash detection and determination of the dressing, qualitative test of the nature of the fibre, quantitative determination of the different kinds of fibre in the sample, investigation of the nature of the dye and of its fastness, determination of the nature and extent of the waterproofing, detection and estimation of the weighting of silk, and distinction between certain crude and bleached products. The methods used are as follows. 

The researcher, by the very nature of his/her work, must constantly deal with chemical reactivity and determine the appropriate time to obtain reactive chemicals data. Obviously, each reaction mixture or minute quantity of unknown material cannot be subjected to extensive testing for reaction potential. On the other hand, uncontrolled laboratory reactions which may injure people and damage property must be prevented. 

Thus far, this method can be applied only to fabrics since reflectance measurements cannot be made on small quantities of yarns and fibers. All the naturally degraded yarns and fibers gave a qualitatively positive response to Turnbulls Blue test, however. The ubiquitous presence of dirt in the archaeological samples will complicate the use of quantitative chemical tests for determining the state of oxidation. 

Calculational methods for the accurate determination of thermodynamic parameters (particularly for solution-phase calorimetry) have only recently become available through the BCHMP chemical test and reference reaction. It is likely therefore that values reported for enthalpy, for example, are likely to be significantly in error for some of the earlier work using flow calorimetry. These errors can be rectified, however, through the calculation of the thermal volume and relevant adjustment of the calorimetric data. 

A redox reaction involving silver is used in a chemical test to determine whether an unknown organic compound is an aldehyde. This test is called a Tollen s test. It is also sometimes called the silver mirror test because a spectacular shiny layer of elemental silver plates out on the inside of a test tube if an aldehyde is present. In this test, a silver nitrate solution is mixed with a solution of the unknown substance, and the mixture is observed to see whether the mirror forms. 

To insure that a statistical average behavior is observed in the chemical experiments with No and Lr, it has been necessary to make repeated measurements for each data point. Indeed, the determination of the distribution coefficients for Lr in a solvent extraction experiment required over 200 experiments to define the behavior of about 150 atoms of Lr (JL). Experiments of this kind are exceptionally difficult and computer-controlled equipment has been devised to perform either a portion or all of operations needed for the chemical tests and the analysis of samples. Computer automation, although requiring a larger effort to implement, permits an experiment to be repeated many times in rapid sequence with the added advantage of doing each quickly before the complete decay of the radioactive atoms of a shortlived isotope. 

Test and determine the population statistics for sensitivity, interferent resolution and temperature coefficients (electrical and chemical) for 1st generation devices... 

To be able to use the available water, man must test it. He must ascertain whether it can be used for the intended purpose or whether he must switch to another source of water. The simplest form of water analysis is local inspection and sensory examination. Modern methods of water analysis employ complex chemical and physico-chemical separation and determination techniques, in which readings are supplied by measuring instruments working on a variety of measuring principles, as well as microbiological techniques. Electronic data processing systems are used to evaluate the results of the... 

Ionic reactions [91,131], if anything, meet the required accuracy to determine a total amount of liberated amino functions on polymer much better than any covalently reacting analytical chemical. Salt formation of amino groups by protonation with subsequent titration of the anions released after deprotonation is almost the best chemical test to determine quantitatively the total amount of amino functions on polymer support, as long as, first, no other basic centers are present which can become protonated and, secondly, no by-products from prestages of the gel phase synthesis contain or release anions of the type on which the quantitative titration is based. 

A chemical test for determining the presence and amount of protein in a solution. The biuret reagent containing copper sulfate is a bright blue. When the biuret reagent is added to a protein in a strong alkali solution, a blue-violet color is formed due to the reaction of the biuret reagent with the peptide bonds. The intensity depends upon the amount of protein. 

In addition to the tests of radioactivity discussed above purely chemical tests to determine the total amount of, say, chromate or phosphate may also be carried out. Typical preparations, controlled on the principles outlined above, are sodium iodide ( I) injection and solution, sodium phosphate (32p) injection and solution, sodium chromate ( Cr) injection and ferric citrate ( Fe) injection. 

Another study, sponsored by HUD, on the use of sodium sulfide to detect lead in paint is being carried out at NIST. The objectives of this study include (1) investigating additional candidate procedures for carrying out a field chemical test and (2) determining estimates of the precision and accuracy of a potential candidate alternative procedure and a swab spot test procedure, when carried out by trained lead-based paint inspectors. 

Before the widespread availability of instrumental methods the major approach to structure determination relied on a battery of chemical reactions and tests The response of an unknown substance to various reagents and procedures provided a body of data from which the structure could be deduced Some of these procedures are still used to supple ment the information obtained by instrumental methods To better understand the scope and limitations of these tests a brief survey of the chemical reactions of carbohydrates is m order In many cases these reactions are simply applications of chemistry you have already learned Certain of the transformations however are unique to carbohydrates... 

The aroma of fmit, the taste of candy, and the texture of bread are examples of flavor perception. In each case, physical and chemical stmctures ia these foods stimulate receptors ia the nose and mouth. Impulses from these receptors are then processed iato perceptions of flavor by the brain. Attention, emotion, memory, cognition, and other brain functions combine with these perceptions to cause behavior, eg, a sense of pleasure, a memory, an idea, a fantasy, a purchase. These are psychological processes and as such have all the complexities of the human mind. Flavor characterization attempts to define what causes flavor and to determine if human response to flavor can be predicted. The ways ia which simple flavor active substances, flavorants, produce perceptions are described both ia terms of the physiology, ie, transduction, and psychophysics, ie, dose-response relationships, of flavor (1,2). Progress has been made ia understanding how perceptions of simple flavorants are processed iato hedonic behavior, ie, degree of liking, or concept formation, eg, crispy or umami (savory) (3,4). However, it is unclear how complex mixtures of flavorants are perceived or what behavior they cause. Flavor characterization involves the chemical measurement of iadividual flavorants and the use of sensory tests to determine their impact on behavior. 

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