Preliminary examination of a mixture

A water-soluble mixture may be in the form of a mixture of water-soluble solids or in the form of a liquid. The liquid mixtures are frequently aqueous solutions. The preliminary examination of a hquid mixture (see 1) will indicate whether a volatile solvent (i.e., removable on a boiling water bath) is present. If a volatile solvent is present, distil 20 g. of the mixture from a water bath until no more hquid passes over set aside the volatile solvent for identification. Dissolve the residue (B) in water as detailed below for a mixture of sohds. 

A preliminary investigation was made of the toxicity of the graft copolymer emulsion using human erythrocytes as a model cell line. First of all the toxicity of an emulsion prepared from 5% HEMA and 1% alginate in phosphate buffered saline was estimated by examination of a mixture with 10% hematocrit after 1 h storage. No lysis could be observed and the cells could be separated and disrupted in distilled water. We then encapsulated 10% hematocrit in the same emulsion and stored the capsules in isotonic saline for one week. The cells were recovered by disruption of the capsules with citrate and were perceived as healthy as per the simple tests outlined above. 

In addition, additive effects that are difficult to assess must also be considered. Examinations of mixtures have provided preliminary information. They show that although the intensities of compounds with a similar aroma note add up, the intensity of the mixture is usually lower than the sum of the individual intensities (cf. 3.2.1.1). For substances which clearly differ in their aroma note, however, the odor profile of a mixture is composed of the odor profiles of the components added together, only when the odor intensities are approximately equal. If the concentration ratio is such that the odor intensity of one component predominates, this component then largely or completely determines the odor profile. 

A given unknown appeared to be pure since the boiling-point was fairly constant at 198°-199° while preliminary examination and solubility test gave no indication of a mixture. By means of the usual systematic tests the unknown was limited to the class of primary aromatic amines, and consultation of the tables (page 200) suggested the following individual possibilities ... 

The laboratory work in this part of the course will include a study of two or three relatively simple mixtures, each consisting of from two to six components. The identification of these mixtures will require a thorough mastery of the preceding work, espe-ciallj - since it is impossible to outline a set of procedures that may be applied directly to the gi-eat vaiiety of combinations that may be met. More or less specific instructions may be given, however, concerning the preliminary examination of mixtures. 

In outlining methods for the preliminary examination, we shall limit ourselves to two types of mixtures ( ) water-insoluble and (6) water-soluble. Xaturally, many mixtures will fall in an intermediate field, some of the ingredients being water-soluble and others insoluble in water. Alcoholic solutions of tvater-insoluble compounds furnish a very common example of this tyj e. Frequently the solubility in water of certain ingredients will be appreciably affected by the presence of other compounds, particularly by solvents. It is felt, however, that a study of the common methods of attack of the two extremes will enable the student to deal effectively with intermediate types also. Occasionally, it may be necessary to conduct preliminary examinations on both the water-soluble and the water-insoluble parts of a mixture such examinations are not conducted independently but the results found in the examination of one fraction are used to facilitate the study of the other. 

To IDENTIFY the components of a mixtiure it is first necessary to isolate them in a pure condition. The procedure for separation of the components depends upon their natures, so that no definite scheme can be compiled to cover all possibilities. However, much information can be obtained from a preliminary examination of the mixtiu-e, and as a general rule it is advisable that a mixture should be examined as described in the preliminary tests (pages 17-39), with special reference to the solubility section, and with the following modifications ... 

In this section first some preliminary study is made of the robustness of some mixture compositions. After that a systematical examination of the design space is performed. 

When commencing a fractional crystallisation, preliminary tests similar to those described under Crystallisation are first carried out, and the crystals which separate during such tests examined with a lens. The crystals which form first are either the least soluble or most abundant constituent of the mixture. If a second or further type of crystal appears, its shape and time of formation relative to cooling should be noted it is often necessary to filter off the first crop while the mixture is still warm. 

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