Лако-красочные материалы — производство

Accurate analytical determination of starting materials is essential in the dye industry. The methods which are used are partly physical, partly chemical. With many products, only physical data, such as melt­ing point, freezing point, and boiling poiqt, are determined. Thus, aniline, toluidine, nitro compounds, and many others, are characterized solely by these measurements. In some cases, the specific gravity (dens­ity) and even the refractive index to monochromatic light are deter­mined. All the important methods are given in the valuable work of Lunge (Untersuchungsmethoden). The specifications are often estab­lished by agreement and variations from them serve for guidance. Today, intermediates are marketed in such high purity that no reasonable de­mands are unfulfilled.

Test samples of materials which are purchased should be investi­gated without delay in the analytical laboratory. The sampling is fre­quently specified in the purchase contract, as are the methods of heating to be used in melting point and freezing point determinations. Materials prepared in the plant are frequently used in technical solutions whose content of active material is determined by analysis. The large firms are going over more and more to the practice of weighing out their solutions directly into the reaction vessels, using balances with a total capacity of up to 40,000 kilograms and a sensitivity of 100 grams.

The molecular weight, calculated from the chemical formula, is given as a characteristic for each product in the dye industry. Now, many substances are used in different forms, e. g., benzidine as the sul­fate and as the free base, and Gleve acids as the free acids and as the sodium salts. It is agreed, therefore, always to take the same value for molecular weight, whereby, of course, a salt comes out with a lower purity than the free acid. The molecular weight of any material pur­chased is always specified along with the price per kilogram of pure material. For example, if 1 kilogram of benzidine (mol. wt. 184) costs 3 frs., and 1 kilogram of benzidine sulfate (mol. wt. 282) costs 2 frs.,

then the pure base in benzidine sulfate costs 2 x 282/184 or 3.02 frs. The cost of the base is therefore identical in the two products. In the above example, the sulfate would be 65.2 per cent pure (mol. wt. 184), and to obtain 184 kilograms of benzidine base, 282 kilograms of the sulfate would have to be used.