The solution of the purified linters is of great importance, since the quality of the finished product depends to a considerable extent on proper attention to that process. The cotton is put into the cuprammonium liquid in large iron dissolvers and stirred continuously. Eventually, a thick and viscous solution is obtained, of a deep blue colour, smelling strongly of ammonia and easily drawn into threads. However, it is not yet ready for spinning. It is inevitable that the linters should still contain traces of dirt which, although too fine to be removed by the initial cleansing processes, would stop up the fine holes of the spinning apparatus and produce faulty filaments. In addition, a certain amount of air is present in the solution which would interfere with the spinning process. The solution is therefore filtered and the air extracted. Now it is ready for use and comes into the stock container, from which it is withdrawn for spinning.
After passing through a pipe, the solution arrives at a metal headpiece—the nozzle head—on which is fixed a metal disc with small holes. The whole thing, headpiece and nozzle, is fitted into a glass cylinder which has a metal ring top and bottom. A glass funnel, the lower end of which is connected with a small glass thimble, is also set into the cylinder and the complete apparatus forms the spinning funnel. This is fed continuously with a coagulating liquid called the spinning bath, which, after filling the entire spinning-funnel, runs off through the small glass thimble. With suitable pressure, the spinning solution is forced through fine orifices in a metal disc and arrives in the spinning bath. The stream of coagulating solution draws the separate filaments down the funnel; they pass through the small glass thimble and are then wound onto a rotating wheel in the form of thread. The thickness of the thread depends on the volume of spinning solution supplied and on the length which is drawn away from the nozzle by the reel.
The spinning bath acts on the filaments in such a way as to wash out the ammonia and copper. Both chemicals, however, are necessary to keep the cellulose in its dissolved form, for as soon as the ammonia and copper are removed, the filaments coagulate. They must, however, pass through the intermediate stages between these two extremes; they must harden slowly as they sink deeper into the funnel. Their downward movement is