After being wrung, squeezed or hydro-extracted the goods are ready to be dried. In the case of yarns this may be done in rooms heated by steam pipes placed on the floor, the hanks being hung on rods suspended from racks arranged for the purpose.
Where large quantities of yarn have to be dried it is most economical to employ a yarn or drying machine, and one form of such is shown in figure 31. 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 low. 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 subject drives off the water it contains. The yarn requires no attention from 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 the dried yarn. The machine works regularly and well.
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 moisture they contain, and the water-charged air thus produced must be taken away as quickly as possible.
Piece Goods.--The most convenient manner of drying piece goods is to employ the steam cylinder drying machine such as is shown in figure 32. 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.
CHAPTER VIII.
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 50 grammes 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 gramme weights and to get accustomed to them, which is not by any means difficult.