It may also be noted that by alkylating Primuline handsome yellow basic and acid dyes are formed which have not, however, any great importance.

Naphthamine Yellow NN.

Formula:

Dehydrothiotoluidine-sulphonic acid.

-N=N-

Dehydrothiotoluidine-sulphonic acid.

67.4Gms. (2/10 mol.) of pure 100 % ammonium salt of molecular weight 337, corresponding to 14 gms. sodium nitrite, are dissolved in exactly 8.2 gms. 100 % caustic soda, and 300 c.cs. water, and the ammonia is then boiled off, as even traces of ammonia upset the oxidation. After an hour, when the odour of ammonia has disappeared, the solution is made up to 500 c.cs. at 20o, and is mixed with 10.5 gms. Hc10 in the form of an approximately 5 % sodium hypochlorite solution. Both the ammonium salt and the hypochlorite must be exactly determined by titration. The temperature rises about 40 and after 1 hour a small test-portion is heated in a test-tube and salted out. The precipitate must be a pure orange, and potassium-iodide-starch-paper should show clearly the presence of hypochlorous acid. If this is not found to be the case a further quantity of hypochlorite is added. After standing for 5 hours, the mixture is boiled up, precipitated with 15 % of common salt, and the product filtered off. Yield about 75 gms. strong dye.

67.4 gms. 100 % Nh4 salt.

8.2 gms. NaOH. About 300 c.cs. H2O.

1 Erika Z of the Berlin Aniline Co. is the combination: Dehydro-thioxyli-dine + є-acid. Similar dyes are obtained from naphthol disulphonic acid 1:3:6.

Naphthamine Yellow NN is the fastest to light of all yellow cotton dyes, and is completely stable towards chlorine. For this reason it is used in large quantities in the United States, where the washing is always treated with bleaching agents. It is not so pure as Chryso-phenine, and is inferior to it as regards strength.

10.5 gms. 100 % Hcio.

Thiazole Yellow or Clayton Yellow.

Formula:

Dehydrothiotoluidine-sulphonic acid.

-N2-NH-

Dehydrothiotoluidine -sulphonic acid.

An amount of dehydrothiotoluidine-sulphonic acid corresponding to 14 gms. sodium nitrite are dissolved in 25 gms. 30 % caustic soda, and the solution is divided into two equal parts, one of which is acidified with 25 c.cs. concentrated hydrochloric acid. It is diazo-tized at io° during 2 hours with 7 gms. of 100 % sodium nitrite. The orange-yellow diazo-compound is then run into the other half of the sulphonic acid, to which a further 25 gms. dehydrated sodium carbonate in a little water and 25 c.cs. strong ammonia have been added. The temperature during the coupling should be 4-5°, and it is advisable to keep the solution as concentrated as possible. After 2 hours the liquid is heated up to 30o and allowed to stand over-night. Next day it is heated up to 8o° and salted out with 20 % of salt. The yield of strong dye is about 85 gms.

Thiazole Yellow (Clayton Yellow, Mimosa, etc.) is, in contrast to Chloramine Yellow, the most fugitive yellow in the whole dye industry, and it is a matter for surprise that such a product should ever have been used at all.

Thiazole Yellow is altered by caustic soda solution from a pure yellow to a bright red, for which reason it is used as a reagent for caustic alkali (see " Thiazole paper "). As already mentioned, it is

14 gms. Nitrite dehydrothiotoluidine-sulphonic acid. 25 gms.

50% NaOH.

25 c.cs.

30%

Hc1.

7 gms.

NaNo2.

25 gms. Na2Co3. 25 c.cs.

20%

Nh3.

extremely loose, but possesses great purity and strength, so that it is, unfortunately, used for dyeing cheap qualities of textile goods.

On sulphonating colour bases of the Primuline type by the "bake process," sulphonic acids are obtained which form azo colours faster to light than those prepared from the ordinary sulphonic acid. It is assumed that on "baking" the sulphonic group enters in the o-position to the amino group, by which means the fastness to light is considerably increased; attention has already been called to this relationship in connection with the pyrazolone colours.

Notes on Works Technique and Practice. - The preparation of the Primuline melt is carried out in pots heated in an oil-bath and provided with reflux condensers which are filled with hot water to prevent the p-toluidine which sublimes from stopping up the tubes. The hydrogen sulphide is collected in caustic soda solution and used for reductions. In the early days of the manufacture of Primuline the hydrogen sulphide was simply burnt under the boiler, which is a thoroughly irrational proceeding and distinctly unpleasant for the neighbourhood. The extraction with alcohol is carried out in iron boilers provided with perforated bottoms so that the alcohol may be constantly redistilled and used again as in a Soxhlet extraction apparatus. After distilling off the alcohol from the extract the residue is reheated in the oil-heated boiler to 240o until toluidine ceases to be evolved.

Analogous products to Chloramine Yellow, Thiazole Yellow, etc., may also be prepared from Primuline itself, but these colours are much redder, weaker, and duller in shade, so that they are little in demand.