FIG. 41.--Automatic Yarn-dryer.FIG. 41.—Automatic Yarn-dryer.
Where large quantities of yarn have to be dried, it is most economical to employ a yarn-drying machine, and one form of such is shown in Fig. 41. The appearance of the machine is that of one long room from the outside; internally it is divided into compartments, each of which is heated up by suitably arranged steam pipes, but the degree of heating in each compartment varies—at the entrance end it is high, at the exit end lower. The yarn is fed in at one end, being hung on rods, and by suitable gearing it is carried directly through the various chambers or sections, and in its passage the heat to which it is subjected drives off the water it contains. The yarn requires no attentionfrom the time it passes in wet at the one end of the machine and comes out dry at the other end. The amount of labour required is slight, only that represented by filling the sticks with wet yarn and emptying them of the dried yarn. The machine works regularly and well.
FIG. 42.--Truck Yarn-dryer.FIG. 42.—Truck Yarn-dryer.
The drying is accomplished by circulating heated air through the yarns, this heating being effected by steam coils, fresh air continually enters the chambers, while water-saturated air is as continually being taken out at the top of the chamber. One of the great secrets in all drying operations is to have a constant current of fresh hot air playing on the goods to be dried; this absorbs the moisturethey contain, and the water-charged air thus produced must be taken away as quickly as possible.
FIG 43.--Drying Cylinders.FIG 43.—Drying Cylinders.
Fig. 42 shows what is called a truck yarn-dryer, which consists of a chamber heated with steam pipes and fitted with an exhausting fan to draw out the air and water vapour which is produced. The yarns are hung on truckswhich can be run in and out of the chamber for filling and emptying.
Piece Goods.—The most convenient manner of drying piece goods is to employ the steam cylinder drying machine, such as is shown in Fig. 43. This consists of a number of hollow tin or copper cylinders which can be heated by steam passing in through the axles of the cylinders, which are made hollow on purpose. The cloth to be dried passes round these cylinders, which revolve while the cloth passes. They work very effectually. The cylinders are arranged sometimes, as in the drawing, vertically; at other times horizontally.
TESTING OF THE COLOUR OF DYED FABRICS.
It is frequently desirable that dyers should be able to ascertain with some degree of accuracy what dyes have been used to dye any particular samples of dyed cloth that has been offered to them to match. In these days of the thousand and one different dyes that are known it is by no means an easy thing to do; and when, as is most often the case, two or three dye-stuffs have been used in the production of a shade, the difficulty is materially increased.
The only available method is to try the effect of various acid and alkaline reagents on the sample, noting whether any change of colour occurs, and judging accordingly. It would be a good thing for dyers to accustom themselves to test the dyeings they do, and so accumulate a fund of practical experience which will stand them in good stead whenever they have occasion to examine a dyed pattern of unknown origin.
The limits of this book does not permit of there being given a series of elaborate tables showing the action of various chemical reagents on fabrics dyed with various colours; and such, indeed, serve very little purpose, for it is most difficult to describe the minor differences which often serve to distinguish one colour from another. Instead of doing so, we will point out in some detail the methods of carrying out the various tests, and advise all dyers to carry these out for themselves on samples dyed with knowncolours, and when they have an unknown colour to test to make tests comparatively with known colours that they think are likely to have been used in the production of the dyed fabric they are testing.
One very common method is to spot the fabric, that is, to put a drop of the reagent on it, usually with the end of the stopper of the reagent bottle, and to observe the colour changes, if any, which ensue. This is a very useful test and should not be omitted, and it is often employed in the testing of indigo dyed goods with nitric acid, those of logwood with hydrochloric acid, alizarine with caustic soda, and many others. It is simple and easy to carry out, and only takes a few minutes.
To make a complete series of tests of dyed fabrics there should be provided the following reagents:—
1. Strong sulphuric acid, as bought.
2. Dilute sulphuric acid, being the strong acid diluted with twenty times its volume of water.
3. Concentrated hydrochloric acid.
4. Dilute hydrochloric acid, 1 acid to 20 water.
5. Concentrated nitric acid.
6. Dilute nitric acid, 1 acid to 20 water.
7. Acetic acid.
8. Caustic soda solution, 5 grams in 100 c.c. water.
9. Ammonia (strong).
10. Dilute ammonia, 1 strong ammonia to 10 water.
11. Carbonate of soda solution, 6 grams in 100 c.c. water.
12. Bleaching powder solution, 2° Tw.
13. Bisulphite of soda, 72° Tw.
14. Stannous chloride, 10 grams crystals in 100 c.c. water, with a little hydrochloric acid.
15. Methylated spirit.
Small swatches of the dyed goods are put in clean porcelain basins, and some of these solutions poured over them. Anychange of colour of the cloth is noted, as well as whether any colour is imparted to the solutions. After making observations of the effects in the cold the liquids may be warmed and the results again noted. After being treated with the acids the swatches should be well washed with water, when the original colour may be wholly or partially restored.
To give tables showing the effects of these reagents on the numerous dyes now known would take up too much room and not serve a very useful purpose, as such tables, if too much relied on, leave the operator somewhat uncertain as to what he has before him. The reader will find in Hurst'sDictionary of Coal-tar Colourssome useful notes as to the action of acids and alkalies on the various colours that may be of service to him.
Alizarine and the series of dye-stuffs to which it has given its name, fustic, cochineal, logwood and other dyes of a similar class require the fabric to be mordanted, and the presence of such mordant is occasionally an indirect proof of the presence of these dyes.
To detect these mordants, a piece of the swatch should be burnt in a porcelain or platinum crucible over a Bunsen burner, care being taken that all carbonaceous matter be burnt off. A white ash will indicate the presence of alumina mordants, red ash that of iron mordants, and a greenish ash chrome mordants.
To confirm these the following chemical tests may be applied: Boil the ash left in the crucible with a little strong hydrochloric acid and dilute with water. Pass a current of sulphuretted hydrogen gas through the solution; if there be any tin present a brown precipitate of tin sulphide will be obtained. This can be filtered off. The filtrate is boiled for a short time with nitric acid, and ammonia is added to the solution when alumina is thrown down as a white gelatinous precipitate; iron is thrown down as a brown red bulky precipitate; while chrome is thrown down as a greyish-looking gelatinous precipitate. The precipitate obtained with the ammonia is filtered off, and a drop of ammonium sulphide added, when any zinc present will be thrown down as white precipitate of zinc sulphide: to the filtrate from this ammonium oxalate may be added, when if lime is present a white precipitate of calcium oxalate is obtained.
A test for iron is to dissolve some of the ash in a little hydrochloric acid, and add a few drops of potassium ferrocyanide solution, when if any iron be present a blue precipitate will be obtained.
To make more certain of the presence of chrome, heat a little of the ash of the cloth with caustic soda and chlorate of soda in a porcelain crucible until well fused, then dissolve in water, acidify with acetic acid and add lead acetate; a yellow precipitate indicates the presence of chrome.
A book on qualitative chemical analysis should be referred to for further details and tests for metallic mordants.
The fastness of colours to light, air, rubbing, washing, soaping, acids and alkalies is a feature of some considerable importance. There are indeed few colours that will resist all these influences, and such are fully entitled to be called fast. The decree of fastness varies very considerably. Some colours will resist acids and alkalies well, but are not fast to light and air; some will resist washing and soaping, but are not fast to acids; Some may be fast to light, but are not so to washing. The following notes will show how to test these features:—
Fastness to Light and Air.—This is simply tested by hanging a piece of the dyed cloth in the air, keeping a piece in a drawer to refer to, so that the influence on the original colour can be noted from time to time. If the piece is left out in the open one gets not only the effect of light but also that of climate on the colour, and there is no doubt wind, rain, hail and snow have some influence on the fading of the colour.
If the piece is exposed under glass, the climatic influences do not come into play, and one gets the effect of light alone.
In making tests of fastness, the dyer will and does pay due regard to the character of the influences that the material will be subjected to in actual use, and these vary very considerably; thus the colour of underclothing need not be fast to light, for it is rarely subjected to that agent of destruction. On the other hand it must be fast to washing, for that is an operation to which underclothing is subjected week by week.
Window curtains are much exposed to light and air, and, therefore, colours in which they are dyed should be fast to light and air. On the other hand these curtains are rarely washed, and so the colour need not be quite fast to washing. And so with other kinds of fabrics, there are scarcely two kinds which are subjected to the same influences, and require the colours to have the same degree of fastness.
The fastness to rubbing is generally tested by rubbing the dyed cloth on a piece of white paper.
Fastness to Washing.—This is generally tested by boiling a swatch of the cloth in a solution of soap containing 4 grams of a good neutral curd soap per litre for ten minutes and noting the effect—whether the soap solution becomes coloured and to what degree, or whether it remains colourless, and also whether the colour of the swatch has changed at all.
One very important point in connection with the soaping test is whether a colour will run into a white fabric that may be soaped along with it. This is tested by twisting strands of the dyed yarn or cloth with white yarn or cloth and boiling them in the soap liquor for ten minutes and then noting the effect, particularly observing whether the white pieces have taken up any colour.
Fastness to acids and fastness to alkalies is observed while carrying out the various acid and alkali tests given above.
EXPERIMENTAL DYEING AND COMPARATIVE DYE TESTING.
Every dyer ought to be able to make experiments in the mordanting and dyeing of textile fibres for the purpose of ascertaining the best methods of applying mordants or dye-stuffs, the best methods of obtaining any desired shade, and for the purpose of making comparative tests of dyes or mordanting materials with the object of determining their strength and value. This is not by any means difficult, nor does it involve the use of any expensive apparatus, so that a dyer need not hesitate to set up a small dyeing laboratory for fear of the expense which it might entail.
In order to carry out the work indicated above there will be required several pieces of apparatus. First, a small chemical balance, one that will carry 100 grams in each pan is quite large enough; and such a one, quite accurate enough for this work, can be bought for 25s. to 30s., while if the dyer be too poor even for this, a cheap pair of apothecaries' scales might be used. It is advisable to procure a set of gram weights, and to get accustomed to them, which is not a very difficult task.
In using the balance always put the substance to be weighed on the left-hand pan, and the weights on the right-hand pan. Never put chemicals of any kind direct on the pan, but weigh them in a watch glass, small porcelain basin, or glass beaker, which has first been weighed,according to the nature of the material which is being weighed. The sets of weights are always fitted into a block or box, and every time they are used they should be put back into their proper place.
The experimenter will find it convenient to provide himself with a few small porcelain basins, glass beakers, cubic centimetre measures, two or three 200 c.c. flasks with a mark on the neck, a few pipettes of various sizes, 10 c.c., 20 c.c., 25 c.c.
The most important feature is the dyeing apparatus. Where only a single dye test is to be made, a small copper or enamelled iron saucepan, such as can be bought at any ironmonger's, may be used; this may conveniently be heated by a gas boiling burner, such as can also be bought at an ironmonger's or plumber's for 2s.
FIG. 44.--Experimental Dye-bath.FIG. 44.—Experimental Dye-bath.
It is, however, advisable to have means whereby several dyeing experiments can be made at one time and under precisely the same conditions, and this cannot be done by using the simple means noted above.
To be able to make perfectly comparative dyeing experiments it is best to use porcelain dye-pots—these may be bought from most dealers in chemical apparatus—and to heat them in a water-bath arrangement.
The simplest arrangement is sketched in Fig. 44; it consists of a copper bath measuring 15 inches long by 10½inches broad and 6½ inches deep—this is covered by a lid in which are six apertures to take the porcelain dye-baths. The bath is heated by two round gas boiling burners of the type already referred to.
The copper bath is filled with water, which, on being heated to the boil by the gas burners, heats up the dye liquids in the dye-pots. The temperature in the dye-pots under such conditions can never reach the boiling point; where it is desirable, as in some cases of wool mordanting and dyeing, that it should boil, there should be added to the water in the copper bath a quantity of calcium chloride, which forms a solution that has a much higher boiling point than that of water, and so the dye liquors in the dye-pots may be heated up to the boil.
An objection might be raised that with such an apparatus the temperature in every part of the bath may not be uniform, and so the temperature of the dye-liquors in the pots may vary also, and differences of temperature often have a considerable influence on the shade of the colour which is being dyed. This is a minor objection, which is more academic in its origin than of practical importance. To obviate this Mr. William Marshall of the Rochdale Technical School has devised a circular form of dye-bath, in which the temperature in every part can be kept quite uniform.
The dyeing laboratories of technical schools and colleges are generally provided with a more elaborate set of dyeing appliances. These, in the latest constructed, consist of a copper bath supported on a hollow pair of trunnions, that the bath can be turned over if needed. Into the bath are firmly fixed three earthenware or porcelain dye-pots; steam for heating can be sent through the trunnions. After the dyeing tests have been made the apparatus can be turned over, and the contents of the dye-pots emptied into a sink which is provided for the purpose.
Many other pieces of apparatus have been devised and made for the purpose of carrying on dyeing experiments on the small scale, but it will not be needful to describe these in detail. After all no more efficient apparatus can be desired than that described above.
Dyeing experiments can be made with either yarns or pieces of cloth—swatches, as they are commonly called—a very convenient size is a small skein of yarn or a piece of cloth having a weight of 5 grams. These test skeins or pieces ought to be well washed in hot water before use, so that they are clean and free from any size or grease. A little soda or soap will facilitate the cleansing process.
In carrying out a dyeing test the dye-pot should be filled with the water required, using as little as can be consistent with the dye swatch being handled comfortably therein, then there is added the required mordants, chemicals, dyes, etc., according to the character of the work which is being done.
Of such chemicals as soda, caustic soda, sodium sulphate (Glauber's salt), tartar, bichromate of potash, it will be found convenient to prepare stock solutions of known strength, say 50 grams per litre, and then by means of a pipette any required quantity can be conveniently added. The same plan might be followed in the case of dyes which are constantly in use, in this case, 5 grams per litre will be found strong enough.
Supposing it is desired to make a test of a sample of direct red, using the following proportions: 2 per cent. dye-stuff, 3 per cent. soda, 15 per cent. Glauber's salt, and the weight of the swatch which is being used is 5 grams. The following calculations are to be made to give the quantities of the ingredients required.
For the dye-stuff:—
5 (weight of swatch) multiplied by 2 (per cent. of dye) and divided by 100 equals—
5 x 2
——— = 0.1 gram dye
100
For the soda we have similarly:—
5 x 3
——— = 0.15 gram soda.
100
For the Glauber's salt:—
5 x 15
———— = 0.75 gram Glauber's salt.
100
These quantities may be weighed out and added to the dye-bath, or if solutions are kept, a calculation can be made as to the number of cubic centimetres which contain the above quantities, and these measured out and added to the dye-bath.
When all is ready, the bath is heated up, the swatch entered, and the work of the test entered upon.
Students are recommended to make experiments on such points as:—
The shades obtained by using various proportions of dye-stuffs.
The influence of various assistants—common salt, soda, Glauber's salt, borax, phosphate of soda—in the bath.
The influence of varying proportions of mordants on the shade of dyeing.
The value of various assistants, tartar, oxalic acid, lactic acid, sulphuric acid, on the fixation of mordants.
The relative value of different tannin matters, etc.
Each dyer should make himself a pattern-book into which he should enter his tests, with full particulars as to how they have been produced at the side.
It is important that a dyer should be able to makecomparative dye tests to ascertain the relative strength of any two, or more samples of dyes which may be sent to him. This is not difficult, but requires considerable care in carrying out the various operations involved.
Of each of the samples of dyes 0.5 gram should be weighed out and dissolved in 100 c.c. of water, care being taken that every portion of the dye is dissolved before any of the solution is used in making up the dye-vats. Care should also be taken that the skeins of yarn or swatches of cloth are exactly equal in weight; that the same volume of water is placed in each of the dye-pots; that the same amount of sulphate of soda or other dye assistants are added; that the quantities of dye-stuff and solutions used are equal; in fact, that in all respects the conditions of dyeing are exactly the same, such, in fact, being the vital conditions in making comparative dye tests of the actual dyeing strength of several samples of dyes.
After the swatches have been dyed they are rinsed and then dried, when the depth of shade dyed on them may be compared one with another. To prevent any mistakes, it is well to mark the swatches with one, two, three or more cuts as may be required.
It is easier to ascertain if two dyes are different in strength of colour than to ascertain the relative difference between them. There are two plans available for this purpose—one is a dyeing test, the other is a colorimetric test made with the solutions of the dyes.
Dyeing Test.—This method of ascertaining the relative value of two dyes as regards strength of colour is carried out as follows: A preliminary test will show which is stronger than the other. Then there is prepared a series of dye-vats—one contains a swatch with the deepest of the two dyes, which is taken as the standard; the others, swatches with the other dye, but containing 2, 5 and 10 per cent. more dyestuff, and all these swatches are dyed together, and after drying a comparison can be made between them and the standard swatch and a judgment formed as to the relative strength of the two dyes. A little experience will soon enable the dyer to form a correct judgment of the difference in strength between two samples of dye-stuff.
Colorimetric Test.—This is based on the principle that the colour of a solution of dye-stuff will be proportionate to its strength. Two white glass tubes equal in diameter are taken. Solutions of the dye-stuff, 0.5 gram in 100 c.c. of water, are prepared, care being taken that the solution is complete. Of one of these solutions 5 c.c. is taken and placed in one of the glass tubes, and 5 c.c. of the other solution is placed in the other glass tube. Of water 25 c.c. is now added to each tube, and then the colour of the diluted liquids is compared by looking through them in a good light. That sample which gives the deeper solution is the stronger in colouring power. By diluting the stronger solution with water until it is of the same depth of colour as the weaker, it may be assumed that the depth of the columns of liquid in the two tubes is in proportion to the relative strength of the two samples. Thus, if in one tube there are 30 c. of liquid and in the other 25 c., then the relative strength is as 30 to 25; and if the first is taken as the standard at 100, a proportion sum gives
30 : 25 : : 100 : 83.3,
that is, the weaker sample has only 83.3 per cent, of the strength of the stronger sample.