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analysis submitted, use has been made, in the first place, of methods for ascertaining the dyeing property of the dyestuff's on the fibre, such tests (so-called "stripping tests") being an inversion of the respective dyeing process. In the second place, in order to ascertain the chemical relationship of the dyestuff, a modification of the method suggested by the author in 1893 for the analysis of dyestuffs in substance has been employed, which depends upon the different behavior of the respective leuco compounds to oxidation. This method consisted in reducing the dyestuff with zinc dust, and reoxidation by air and chromic acid. Whilst nitro, nitroso, and azo compounds were completely destroyed on reduction, those dyestuffs which may be regarded as having an ortho quinonoid structure gave leuco compounds which were readily reoxidized by air to the original dyestuffs, and those to which a para quinonoid structure is attributable gave leuco compounds stable to air but reoxidized by chromic acid. A still further group of dyestuffs were not reducable at all, and the alizarine colors were changed to red or brown but not decolorized. It has been ascertained that these reactions can be satisfactorily performed upon the wool or silk fibre if sodium hydrosulphite is used as the reducing agent, and potassium persulphate as the oxidizing agent. Contrary to what might have been anticipated, the leuco compounds formed remain in great part attached to the fibre, whilst the splitting-products of the azo dyestuffs can be entirely removed therefrom by washing.

The reactions are therefore in many cases sharper than when carried out in substance, as there is no disturbing factor due to secondary oxidation products. The substitution of a persulphate for chromic acid was found to be advantageous on account of the color of the latter.

The following is the general behavior of the various chemical groups of dyestuffs upon animal fibres towards reduction and oxidation:

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Having ascertained both the dyeing group and the chemical relationship of the coloring matter, and taking the shade also into consideration, the question is usually narrowed down to a single representative or to a choice between a very few closely related dyestuffs. For distinguishing between these the behavior with concentrated sulphuric acid or strong hydrochloric acid can be frequently employed. In the appended tables the sub-division of the groups has been usually omitted as unnecessary, but is given in a few instances (see Table II.) in order to illustrate the general method. For additional confirmation it is well to compare the sample both as to shade and reactions with a dyed pattern of the dyestuff to which it is believed to correspond.

It should be remarked that in a scheme of this description the same degree of definiteness cannot be expected as in a scheme of inorganic analysis, and some variation will be found in the sharpness of the indications with individual dyestuffs. A little practice

and experience will therefore be required before absolute certainty can be obtained.

In the appended tables all the possible groups of dyestuffs are considered, although in individual instances many of them would, be at once excluded on account of the nature of the material or its shade. In such cases, therefore, the analytical, scheme may be much simplified.


The following reagents are employed. It is important that they be used of the strength indicated:


1 c.c. conc. ammonia.

100 c.c. water (soft or distilled).


1 c.c. conc. ammonia.

50 c.c. strong alcohol or methylated spirit.
50 c.c. water.


5 c.c. glacial acetic acid.

95 c.c. water.


50 c.c. strong alcohol or methylated spirit.
50 c.c. water.


10 c.c. conc. hydrochloric acid.

100 c.c. water.


10 g. solid caustic soda in

100 c.c. of solution.


A 10 per cent. solution of hydrosulphite NF (Meister) or hyraedite, i.e., the formaldehyde compound of sodium hydrosulphite. This solution, which is slightly alkaline, is employed in most cases. In a few other cases, however, in which the reduction is more sluggish (e.g., azo yellows), it has been found necessary to employ a slightly acid solution. This is termed

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Prepared by acidifying 200 c.c. of hydrosulphite A with 1 c.c. of glacial acetic acid.


A cold saturated solution of potassium persulphate.


5 g. crystallized sodium acetate.

100 c.c. water.


The reactions are performed in test-tubes with pieces of the material about in. to 1 in. square, which are covered with about 1 in. to 1 in. of the reagent. The tests should be carried out exactly as described. In making “stripping tests" the degree of stripping is judged by comparing the depth of shade remaining with that of the original pattern. The color of the stripping solution is misleading, and can scarcely be relied upon as a guide. It

is found advantageous in boiling with dilute acetic acid and dilute ammonia to repeat the extraction, as a better stripping is thereby obtained, and also with acid dyestuffs any staining of the cotton by the first strong extract is avoided. In testing with dilute ammonia or sodium acetate, the piece is placed in a test-tube with a somewhat smaller piece of white mercerized cotton cloth, and boiled for the time prescribed. If the shade is a pale one, the size of the sample should be increased and that of the cotton diminished. The dilute NH, is replaced by aqueous alcoholic NH, in the case of the violet and black dyestuffs (Tables III. and VII.), as in these cases the acid dyestuffs are less easily extracted, and the cotton is more liable to be stained by them. In making reduction tests, the sample is boiled for from one-quarter to one minute with the hydrosulphite, then rinsed well under the tap, and allowed to lie on white paper for an hour or so. With most dyestuffs which form air-oxidizable leuco compounds, the color returns immediately or in a few minutes, but with others a longer time is required. The reaction is accelerated by exposing the pattern to ammonia vapor. If the color does not return the pattern is heated to boiling in a test-tube with a little water, and potassium persulphate is added drop by drop, carefully avoiding an excess. If this also fails to cause any return of color, the dyestuff is to be regarded as an azo compound. The depth of the restored color varies greatly in different cases; whilst with some dyestuffs the color reappears with nearly its original depth, with others (probably on account of the greater solubility of their leuco compounds) only a slight shade may return. Safranine and its azo derivatives yield on reoxidation of the leuco compound a violet color. This is due to the condensation of the leuco-safranine with the formaldehyde present in the hydrosulphite NF.

The reactions given in the annexed analytical tables were mostly ascertained upon the wool fibre, but from a number of tests that were also conducted for comparison upon silk, we have no reason to believe that the latter fibre will exhibit any variations in behavior. On the other hand, cotton and vegetable fibres require

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