Testing dyestuffs

Testing dyestuffs Testing pigments Test methods... 

In spite of the rationale on which the testing of dyestuffs as antibiotics rested subsequent research re vealed that the antibacterial properties of Prontosil had nothing at all to do with its being a dye In the body Prontosil undergoes a reductive cleavage of its azo linkage to form sulfanilamide which is the sub stance actually responsible for the observed biological activity This is why Prontosil is active in vivo but not in vitro... 

Daylight fluorescent pigments (qv) are considered to be nontoxic. Since they are combinations of polymers and dyestuffs, the combined effect of the ingredients must be taken into account when considering the net toxic effect of these materials. Table 5 gives results of laboratory animal toxicity tests of standard modified melamine—formaldehyde-type pigments, the Day-Glo A Series, and the products recommended for plastic mol ding, Day-Glo Z-series. 

Pagga U, Brown D (1986) The degradation of dyestuffs part II. behaviour of dyestuffs in aerobic biodegradation tests. Chemosphere 15 479 -91... 

Most of the naphthalenic ring amines produced during dye degradation are not commercially available and they could not be tested but, they should be oxidized by Fenton chemistry with the same degree of difficulty than the previous dyestuff studied. 

Because of the large number of dyestuffs and the fact that most of these colorants have not been tested for carcinogenicity, structure-activity theory may help predict possible candidates Tor study. 

Such systematic methods, described below in their general outlines, allow the nature of a dyestuff to be orientated and the group to which it belongs determined its precise definition is not, however, easy in all cases, especially since new colouring matters are continually being put on the market. For such identification, use must be made of the reactions and tests to be found in special textbooks.1... 

In the tests with dilute acetic add or dilute ammonia, the extraction should be repeated on the same piece of fabric with the view of completing the extraction and also because it sometimes happens that, in the first boiling with dilute ammonia, certam add dyestuffs dye white cotton, whilst during the second boiling such coloration assumed by the cotton in the first treatment disappears. When boiling with white cotton is prescribed, a... 

Stripping test for acid colours. Some direct or " salt dyestuffs are partly decolorised by dilute ammonia and hence might be regarded as add colouring matters. To avoid this error it is useful to add, when this test is made, a piece of mercerised white cotton. With an add dye, the cotton remains white, or is scarcely coloured, and then becomes white again when boiled a second time with dilute ammonia. 

Tannin test for basic dyestuffs. The extract obtained with formic acid is shaken with a few drops of tannin solution, and if no precipitate forms immediately, the liquid is left at rest for a few minutes. Certain colouring matters, such as the rhodamines, the gallocyanins and the chrome colours of the rosaniline series (containing carboxyls or hydroxyls besides the basic groups) precipitate slowly and the precipitate, being highly subdivided, is sometimes difficult to see. 

Test for sulphide dyestuffs. The sample is covered in a test-tube or conical flask with the acid stannous chloride solution, the mouth of the vessel being closed with a piece of filter-paper steeped in lead acetate solution and the liquid heated slowly to boiling. The appearance of a blackish-brown stain on the filter-paper indicates a sulphur dyestuff. The boiling should not be too protracted, since otherwise the hydrochloric acid vapours may cause the brown lead sulphide to disappear. 

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