The purer the beta-naphthol the better, especially for producing the paranitroaniline red. Various preparations of beta-naphthol have been brought out by colour makers.
The process of dyeing cotton with a naphthol colour takes place in two stages, the first being the grounding or preparing with the naphthol, the second the developing with the diazotised base. Some of the effects which can be obtained from the two naphthols and various bases are given in the following table:--
Base. With beta-naphthol, gives With alpha-naphthol, gives 1. Aniline, Orange yellow; Cutch brown.
2. Paratoluidine, Full yellow orange; Cutch brown.
3. Metanitroaniline, Fiery yellowish red; Brownish orange.
4. Paranitroaniline, Bright scarlet; " "
5. Nitroparatoluidine, Orange; Very bright catechu.
6. Alpha-naphthylamine, Bluish claret red; Reddish puce.
7. Beta-naphthylamine, Turkey red; "
8. Amidoazobenzene, Red; "
9. Orthoamidoazotoluene, Yellowish claret red; "
By mixing alpha-and beta-naphthols together a variety of grenat and claret reds and browns can be obtained.
With regard to the fastness of the shades produced the following may be considered:--
_Fast to Soaping._
Combination of A-Naphthol with Toluidine.
" " A-Naphthylamine.
" " B-Naphthylamine.
" " Amidoazobenzene.
" B-Naphthol with Toluidine.
" " Paranitroaniline.
" " Nitroparatoluidine.
" " B-Naphthylamine.
" " A-Naphthylamine.
_Moderately Fast._
Combination of A-Naphthol with Aniline.
" " Paranitroaniline.
" " Orthoamidoazotoluene.
" B-Naphthol with Metanitroaniline.
" " Amidoazobenzene.
_Very Loose._
Combination of A-Naphthol with Paratoluidine.
" " Metanitroaniline.
" " Nitroparatoluidine.
" B-Naphthol with Aniline.
" " Paratoluidine.
" " Orthoamidoazotoluene.
The samples were tested for fastness to light by exposing them for nine days with the following results:--
_Fast._
Combination of A-Naphthol with Aniline.
" " Toluidine.
" " Metanitroaniline.
" " Paranitroaniline.
" " Nitroparatoluidine.
" " B-Naphthylamine.
" " Amidoazobenzol.
" " Orthoamidoazotoluol.
" B-Naphthol with Aniline.
" " Paratoluidine.
" " Metanitroaniline.
" " Paranitroaniline.
" " B-Naphthylamine.
" " A-Naphthylamine.
_Moderately Fast._
Combination of B- Naphthol with Nitroparatoluidine.
_Very Loose._
Combination of A-Naphthol with Toluidine.
" " A-Naphthylamine " B-Naphthol with Toluidine.
" " Amidoazobenzene.
" " Orthoamidoazotoluene.
The most important of the naphthol colours is undoubtedly paranitroaniline red, produced by the combination of paranitroaniline and beta-naphthol. In order to produce the best and brightest shades these two bodies must be quite pure. The following directions may be followed:--
=Dyeing Paranitroaniline Red on Yarn.=
It unfortunately happens that this red does not admit of being worked in large quantities at a time, particularly in the diazo bath where the colour is developed, as the previous operations seem to render the yarn slightly waterproof, and hence if large quantities of yarn were dealt with at one time some would be found to be dyed all right, others would be defective. It has, therefore, been found best to work only about 2 lb. of yarn at a time, carefully carrying out each operation with this quantity. As, however, the process can be quickly worked it follows that in the course of a day a fairly large quantity of yarn can be treated.
1. _Grounding._ The grounding or preparing bath for 100 lb. of yarn is best made in the following manner: 4 lb. of beta-naphthol are stirred in 2-1/2 lb. of caustic soda liquor 70 Tw., then 1-1/2 quarts of boiling water is added, when dissolved 1-1/2 quarts of cold water. In a separate vessel dissolve 5 lb. Turkey-red oil in 11 quarts of water, then mix the two liquors together and add sufficient water to make up the whole to 12 gallons.
In working sufficient of this liquor is taken and put into a deep tub in which 2 lb. of yarn can be conveniently worked. It is best to work at a tepid heat, say 100 to 110 F.; 2 lb. of the yarn are worked in this liquor, so that it becomes thoroughly impregnated, then it is gently wrung out and hung up. This operation is repeated with each 2 lb. until the whole 100 lb. has been treated, adding from time to time some of the naphthol liquor to make up for that taken up by the cotton. When all the yarn has been through the liquor, give it another dip through the same liquor. Place the yarn in a hydro-extractor for five to seven minutes.
Next open out the yarn well, and hang on sticks and dry in a stove at 140 to 150 F. The stove should be heated with iron pipes, through which steam at 30 lb. to 40 lb. pressure passes. This stove should be reserved entirely for this work, for if other goods be dried in it along with the naphthol-prepared cotton, any steam or acid vapours which might be given off from the former might damage the latter.
When thoroughly dry the yarn is ready for the next operation.
2. _Developing._ The developing bath is made in the following manner: 1-1/2 lb. paranitroaniline is mixed with 1-1/2 gallons of boiling water, and 1-3/4 quarts of hydrochloric acid at 30 to 32 Tw. Stir well until the paranitroaniline is completely dissolved, add 3-1/2 gallons of cold water, which will cause a precipitation of the hydrochlorate of paranitroaniline as a yellow powder. Let the mixture thoroughly cool off, best by allowing to stand all night; 1-1/4 lb. of nitrite of soda is dissolved in 4 quarts of cold water, and this solution is added to the paranitroaniline solution slowly and with constant stirring; in about fifteen to twenty minutes the diazotisation will be complete. At this and following stages the temperature of working should be kept as low as possible. Some dyers use ice in preparing their diazo solutions, and certainly the best results are attained thereby, but with paranitroaniline the ice can be dispensed with. After the end of the time sufficient cold water is added to bring the volume of the liquor up to 10 gallons. This diazo liquor will keep for some days, but it decomposes in time, so that it should not be kept too long.
Another liquor is made by dissolving 4 lb. acetate of soda in 11 quarts of water.
The developing bath is made by taking 4 gallons of the diazo liquor and 1 gallon of the acetate liquor and mixing together, and in this bath the prepared yarn, 2 lb. at a time, is worked. The colour develops immediately. The yarn when dyed is lifted out, wrung, and then it is well washed with water, soaped in a bath at 120 F., with a liquor containing 1/2 oz. soap per gallon, then dried. As the cotton yarn is being passed through the developing bath, the latter is freshened up from time to time by suitable additions of the diazo and acetate liquors in the proportions given above.
Some dyers use a special form of dye vat for dyeing paranitroaniline red on yarn, whose construction can be seen from Fig. 27.