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DISTILLED WATER

is commonly used in laboratories for making chemical reagents and for solvent and washing purposes generally, because ordinary water contains small quantities of mineral substances, and requires, in fact, to be distilled in order to get rid of such impurities.

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DYES AND DYEING

There are an immense number of dyes, some being natural products, such as madder, indigo, logwood, and safflower; but for the most part, they are chemically produced substances from coaltar sources, and the manner in which the dyes become attached to the fabrics also varies according both to the chemical constitution of the fabrics themselves and those of the dyes employed. In some cases, definite compounds are formed by the action of the dyes on the fabrics; in other cases, “lakes” are formed by the action of a mordant, the precipitated substance being thus directly attached to the fabrics, and in yet other casus the dyes are developed on the fibres. Basic dyes, including mauve, magenta, methylene blue, malachite green, and Bismarck brown, are fixed on cotton goods by the use of acidic mordants; acidic dyes,ncluding picric acid, azoscarlets, and aniline blue, are attached to wool and silk goods by the use of an acidbath. Other acidic dyes, such as alizarin red, require the use of a metallic mordant. Dyes of a saline nature, like the Congo red series and primulin, are used for cotton and linen without any mordant, and there are pigment dyes, such as chrome yellow, synthetic indigo, and aniline black, in respect of which the colour is developed on the fibres. The dyestuffs are also classed as “substantive” and “adjective the former have the property of dyeing fibres directly, while the latter will only colour them permanently when used in association with mordants. The socalled “suphur” dyes are largely made from dinitrophenol 20H, “sulphur black” being made from it by the action of sodium sulphide and sulphur. The socalled “ciba” dyes are Indigo derivatives containing bromine. As a ruie, cotton goods will not dye without previous treatment with a mordant, the mordant in such cases directly combining with and thus fixing the dye and the mordants used; for acid dyes, feeble bases like aluminic, c hromic, and ferric hydroxides at e used, the colours of the “lakes” so produced varying with the base employed. Using basic dyes for cotton goods, these are first mordanted with tannic acid or a tin salt, such as the chloride.

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DIOXIDES

Compounds containing two proportions of oxygen to one of baseas, for example, barium dioxide 2

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DIMETHYLANILINE

An oily derivative of aniline which boils at 192 degrees C., has a strong basic character, and is used in the synthetic manufacture of dyes. By a process of mild Oxidation it is converted into methyl violet, and by a process of reduction it yields the dye “malachite green.”

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DISULPHIDES

Compounds containing two proportions of sulphur to one of baseas, for example, rarbon disulphide.

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DYERS BROOM

Found in pastures and thickets in Southern Europe, Russian Asia, Southern Sweden, and some parts of Great Britain; contains two principles, one of which is a yellow colouring matter of crystalline character and another genistein, which can be obtained in the form of colourless crystals.

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DISINFECTANTS

Preparations that destroy in any way the infectants or causes of disease, or render them innocuous.

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DILL OIL

Distilled from the fruit of A net hum graveolens, contains limonene and carvol, has a sp. gr. of from 090 to 092, optical rotation + 70 degrees to 8o degrees, and is soluble in alcohol and ether. It is of pale yellow colour and characteristic odour, and is used in perfumery and for flavouring.

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DUROGLASS

A trade name for borosilicate resistance glassware.

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DIATHERMANOUS

A character of substances like rockcrystal which transmit heat as transparent substances transmit light.

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