54 Gms. o-toluidine (1/2 mol.) are mixed with 24 gms. aniline and then treated with 35 gms. of 30 % Hc1. The mixture is cooled externally to 15o and diazotized at this temperature during 2 hours, with continuous stirring, by means of a concentrated solution of 22 gms. 100 % sodium nitrite, after which the mixture is warmed cautiously during 1 hour to 35o, and is then allowed to stand for at least 10 hours at 30o. 60 C.cs. water are then added, and the product run off from the salt solution, which still contains a little nitrite.

The oily mixture of aniline and aminoazo-toluene is now treated with 180 gms. of 30 % hydrochloric acid and the same quantity of water, 100 gms. iron powder being then sifted in; the temperature should remain below 25°.

The product is kept at this temperature until a test-portion, extracted with a little ether, no longer colours the latter solvent. If this is not the case after an hour a little extra iron is added. The fully reduced solution is now filtered and made up to 600 c.cs. This mixture, containing about one molecule each of aniline, o-toluidine, and p-diamine (mixture of phenylene- and toluylene-diamine) is treated with no gms. finely powdered chalk, and as soon as the evolution of carbon dioxide has ceased, the volume is made up with water and ice to 1 litre. The temperature must not exceed o°. The mixture is now treated during 5 minutes with a solution of 100 gms. sodium bichromate in 400 c.cs. ice-water with stirring, which is continued for a further 12 hours. It is a good thing to leave the mixture over-night, after which it is boiled vigorously either by

54 gms. o-Toluidine, 24 gms. Aniline.

35 gms.

30%

Hc1.

22 gms. 100 % NaNo2.

180 gms. H2O.

180 gms.

30%

Hc1.

About 100 gms. Fe.

110 gms. CaCo3.

100 gms. Na2Cr2O7 400 c.cs Ice-water.

blowing in steam or by heating in a porcelain basin for half an hour. The product is then filtered through a large "nutsch"into a previously warmed jar, and the voluminous residue is washed out with half a litre of boiling water. The clear filtrate is precipitated by means of about 450 gms. salt, added a portion at a time, and the crude Safranine is filtered off after cooling. The colour is still rendered impure by the presence of various by-products, which must be removed. For this purpose the filter-cakes are dissolved in a litre of boiling water and a solution of 2 gms. sodium bichromate in 50 c.cs. of 50 % sulphuric acid is added cautiously until a filtered test-portion appears as pure as Safranine (blue shade). The whole liquid is then filtered, treated with about 15 gms. of dehydrated sodium carbonate (litmus should just be turned blue by the liquid after salting out), and the dye precipitated with 15 % of salt; it is then filtered off, pressed, and dried. Yield of dry product about 40 gms.

The product may be further purified by recrystallizing from water and alcohol. It is a good plan to stir up the moist press-cakes with their own weight of alcohol and then to dissolve up by boiling, a little water being added if necessary. The yield of crystallized Safranine is about 25 gms.

Notes on Works Technique and Practice. - The importance of Safranine has diminished considerably during recent years, and the price has fallen to such an extent that few factories concern themselves with its production. The reduction is also carried out by means of tin and hydrochloric acid, the tin being always recovered by means of zinc dust. With the old process, as already mentioned, the oxidation was effected with recovered manganese dioxide (in presence of oxalic acid). The purification of the dye was carried out by means of sodium sulphate.

The chromic oxide, which is mixed with considerable quantities of iron oxide, cannot be converted directly into chromic salts for tanning purposes, as is the case with that obtained from the manufacture of anthraquinone or of Acid Violet. It is therefore necessary to reconvert the dried residues from the filter-press into calcium-sodium bichromate by treatment with saltpetre and sodium carbonate. This process is carried out either in flat cast-iron roasting pans, or, better, in the well-known rotating oxidizing apparatus. (See, for example, L. Wickop, "Die Herstellung der Alkali Bichromate.")

The Safranines are still used to a fair extent for tannined cotton, and have also a certain importance for paper staining owing to their pure shade and their cheapness.

450 gms, NaCl.

About 1.3 gms. Na2Cr2O7 in 40 c.cs. 50% H2So4.

About 15 gms. Na2Co3.

More yellowish marks are made from mixtures containing more or less aniline. If p-aminodimethylaniline (see Methylene Blue) be used in place of para-toluylene diamine, the bluish Clematines are produced which were formerly utilized in considerable quantities. As the Safranines possess at least one free amino group, they may be diazotized and coupled with various phenols and amines. In this way the important Indoines are formed which are strong basic colours and are used for cotton and wool under various designations (Indoine, Janus Black, etc.).

This will be a suitable point at which to make some further general remarks upon dyes, as in the case of the Safranines and related dyes especially, the conditions connected with their manufacture have altered very considerably in the course of time. It has already been mentioned that the choice of oxidizing agents for the production of Safranine has been dependent upon circumstances. The most suitable oxidizing agent for Safranine disappeared with the gradual diminution of Leblanc soda manufacture. Such more or less voluntary changes in the technology of the artificial organic colouring matters take place almost continuously before our eyes, and it is therefore very important for a colour factory always to possess some unfailing source of supply for any given product, and, on the other hand, to find sufficient outlet for all byproducts.