Лако-красочные материалы — производство

In the organic industrial laboratory the work is almost always done with molecular quantities. Calculations are thus greatly simplified. One — tenth of a gram molecule, or with large molecules one-twentieth, is the commonly used unit in the preparation of end products. This quantity gives enough of the product for the first tests of a dye and its dyeing characteristics. Using this quantity, it is also possible to determine the yield sufficiently accurately, provided that the weighing is done to

0. 1 gram, an accuracy possible with an ordinary pan balance. Smaller amounts (0.01 to 0.02 mole) may be used for more qualitative experi­ments. Starting materials or intermediates, which are to be used in a number of experiments, are usually prepared in quantities of one or two moles. With these amounts, weighing to one gram is sufficiently ac­curate. The technical chemist should become accustomed from the start to weighing or measuring all substances used, even in neutralizations, etc., instead of simply pouring them out of stock bottles. The quantities used should be recorded in his laboratory notebook, because this infor­mation is very necessary if the experiment is to be repeated later.

Many reactions are favored by an excess of one of the reactants, but very often the use of exact stoichiometric quantities is necessary. When a series of experiments is to be carried out, it may be desirable to prepare the required reagents in solutions, containing, for example, one mole in 100, 200, 500, or 1000 cc. In experiments which require special equipment available only in large size, the quantities taken are, of course, adapted to the capacity of the apparatus.

When hydrated, salt-containing, moist, or otherwise impure starting materials are used, their purity must be determined. Some of the usable methods are described in the Analytical Section. The results of such a determination may suitably be expressed, not as per cent, but as the

quantity (M) of the raw material containing one mole of the pure sub­stance. Thus, a value of M of 382 for technical H acid means that 382 grams of the technical material contains one mole of active H acid. Then one knows, without any calculation, that 38.2 grams must be used in an experiment calling for 0.1 mole of H acid, and this quantity is the same whether the technical sample is the free acid or one of its salts, and whether the product is a hydrate or not.