Molecular, generally weights

This is a general method for anionics, but its main use is for determination of molecular (equivalent) weight. The version given here assumes that the method will be used for that purpose. If the molecular weight is known, the drying and weighing step can be omitted, but it is still advisable to determine and correct for any extracted p-toluidine hydrochloride. 

The sampling and elution of such high-molecular-J weight materials requires careful attention in order to avoid quantitative sample losses during the sample in- troduction step. In general, cold injection tech- niques are required for accurate nondiscriminative... 

Resins are generally molecules having aromatic characteristics and contain heteroatoms (N, 0, S, occasionally Ni and V) their molecular weight ranges from 500 to 1000. 

Paraffins consist mainly of straight chain alkanes, with a very small proportion of isoalkanes and cycloalkanes. Their freezing point is generally between 30°C and 70°C, the average molecular weight being around 350. When present, aromatics appear only in trace quantities. 

When an amine, or a solution of its hydrochloride, is added to an aqueous solution of chloroplatinic acid, a salt of the base with the cliloroplatinic acid, of general formula BjiHiPtCle (where B is one molecule of the base) is formed and usually crystallises out, for these chloroplatinates hai e normally a rather low solubility in cold water. The chloroplatinate can be filtered off, dried, and then analysed by direct ignition, when only the metallic platinum ultimately remains. Knowing the percentage of platinum in the chloroplatinate, the molecular weight of the latter, and hence of the constituent base, can readily be calculated. 

If the molecular weight of the aniline is known, the number of amino groups can be calculated alternatively, if the aniline is known to be a monacidic base, its molecular weight can be calculated. If the molecular weight and the acidity of the aniline are both known, then dearly the method can be used to estimate the amount of aniline in a given sample. The method is general for many primary and secondary amines, aniline being used solely as a typical member of the former class. 

The developer is generally a solvent in which the components of the mixture are not too soluble and is usually a solvent of low molecular weight. The adsorbent is selected so that the solvent is adsorbed somewhat but not too strongly if the solvent is adsorbed to some extent, it helps to ensure that the components of the mixture to be adsorbed will not be too firmly bound. Usually an adsorbate adheres to any one adsorbent more firmly in a less polar solvent, consequently when, as frequently occurs, a single dense adsorption zone is obtained with light petroleum and develops only slowly when washed with this solvent, the development may be accelerated by passing to a more polar solvent. Numerous adsorbat are broken up by methyl alcohol, ethyl alcohol or acetone. It is not generally necessary to employ the pure alcohol the addition from 0 5 to 2 per cent, to the solvent actually used suffices in most cases. 

If the ether is a simple one (R — R ), the identification of the resulting alkyl iodide presents no difficulties. If, however, it is a mixed aliphatic ether, the separation of the two alkyl iodides by fractional distillation is generally difficult unless R and R differ considerably in molecular weight and sufficient material is available. 

Thionyl chloride. This reagent (b.p. 76°) is generally used in excess of the theoretical quantity it cannot be employed for acetyd chloride (b.p. 52°) because of the difficulty of separation by fractional distillation. Excellent results are obtained, however, with butyrric acid and acids of higher molecular weight, for example ... 

Mono- and di saccharides are colourless solids or sjrrupy liquids, which are freely soluble in water, practically insoluble in ether and other organic solvents, and neutral in reaction. Polysaccharides possess similar properties, but are generally insoluble in water because of their high molecular weights. Both poly- and di-saccharides are converted into monosaccharides upon hydrolysis. 

Section IV, 135,5), but are unaflFected by the dimedone reagent (Section 111,70, 2). The general reactions are similar to those already given under Aliphatic Ketones (Section 111,74). Owing to their higher molecular weight, such derivatives as oximes and phenylhydrazones are frequently quite satisfactory. 

Styrene-Acrylonitrile (SAN) Copolymers. SAN resins are random, amorphous copolymers whose properties vary with molecular weight and copolymer composition. An increase in molecular weight or in acrylonitrile content generally enhances the physical properties of the copolymer but at some loss in ease of processing and with a slight increase in polymer color. 

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