We have described the processes by which cocoons are ordinarily cooked and brushed, these being the first processes of the filature. Instead of first softening the gum of the cocoons and then attacking the floss with the points of a brush, Mr. Serrell places the cocoons in a receptacle full of boiling water, in which by various means violent reciprocating or vortex currents are produced. The result is that by the action of the water itself and the rubbing of the cocoons one against the other the floss is removed, carrying with it the end of the continuous filament without unduly softening the cocoon or exposing any of the more delicate filament to the rough action of the brush, as has hitherto been the case. The advantages of this process will be readily understood. In brushing after the ordinary manner, the point of the brush is almost sure to come into contact with and to break some of the filament forming the body of the cocoon. When this occurs, and the cocoon is sent to be reeled, it naturally becomes detached when the unwinding reaches the point at which the break exists.
It then has to be sent back, and the end of the filament detached by brushing over again, when several layers of filament are inevitably caught by the brush and wasted, and very probably some other part of the filament is cut. This accounts for the enormous waste which occurs in silk reeling, and to which we have referred. Its importance will be appreciated when it is remembered that every pound of fiber thus dragged off by the brush represents a net loss of about 19s. at the present low prices.
The mechanical details by which Mr. Serrell carries out this process vary somewhat according to the nature of the different cocoons to be treated. In one type of machine the water is caused to surge in and out of a metal vessel with perforated sides; in another a vertical brush is rapidly raised and lowered, agitating the water in a basin, without, however, actually touching the cocoons. After a certain number of strokes the brush is automatically raised, when the ends of the filaments are found to adhere to it, having been swept against it by the scouring action of the water. The cleaning of the cocoons is performed by means of a mechanism also entirely new. In the brushing machinery the floss is loosened and partially detached from the cocoon. The object of the cleaning machine is to thoroughly complete the operation. To this end the cocoons are floated under a plate, and the floss passed up through a slot in the latter. A rapid to and fro horizontal movement is given to the plate, and those cocoons from which the floss has been entirely removed easily give off a few inches of their filament, and allow themselves to be pushed on one side, which is accomplished by the cocoons which still have some floss adhering to them; because these latter, not being free to pay off, are drawn up to the slot in the plate, and by its motion are rapidly washed backward and forward in the water.
This washing soon causes all the cocoons to be freed from the last vestiges of floss without breaking the filament, and after about twenty seconds of movement they are all free and clean, ready for reeling.
We have now to explain the operation of the machine by which the thread is formed from the prepared cocoon. At the risk of some repetition, however, it seems necessary to call attention to the character of the work itself. In each prepared cocoon are about a thousand yards of filament ready to pay off, but this filament is nearly as fine as a cobweb and is tapering. The object is to form a thread by laying these filaments side by side in sufficient number to obtain the desired size. For the threads of raw silk used in commerce, the sizes vary, so that while some require but an average of three filaments, the coarsest sizes require twenty-five or thirty. It being necessary keep the thread at as near the same size as possible, the work required is, in effect, to add an additional cocoon filament to the thread which is being wound whenever this latter has tapered down to a given size, or whenever one of the filaments going to form it has become detached. Those familiar with cotton spinning will understand what is meant when it is said that the reeling is effectively a "doubling" operation, but performed with a variable number of ends, so as to compensate for the taper of the filaments.
In reeling by hand, as has been said, the size of the silk is judged, as nearly as possible, by a complex mental operation, taking into account the number, size, and state of unwinding of the cocoons. It is impossible to do this mechanically, if for no other reason than this, that the cocoons must be left free to float and roll about in the water in order to give off their ends without breaking, and any mechanical device which touched them would defeat the object of the machine. The only way in which the thread can be mechanically regulated in silk reeling is by some kind of actual measurement performed after the thread has left the cocoons. The conditions are such that no direct measurement of size can be made, even with very delicate and expensive apparatus; but Mr. Serrell discovered that, owing to the great tenacity of the thread in proportion to its size, its almost absolute elastic uniformity, and from the fact that it could be stretched, two or three per cent. without injury, it was possible to measure its size indirectly, but as accurately as could be desired. As this fact is the starting point of an entirely new and important class of machinery, we may explain with considerable detail the method in which this measurement is performed.
Bearing in mind that the thread is of uniform quality, it is evident that it will require more force to stretch a coarse thread by a given percentage of its length than it will to stretch one that is finer. Supposing the thread is uniform in quality but varying in size, the force required to stretch it varies directly with the size or sectional area of the thread itself. In the automatic reeling machine this stretch is obtained by causing the thread to take a turn round a pulley of a given winding speed, and then, after leaving this pulley, to take a turn around a second pulley having a somewhat greater winding speed.