Until about 1840, much difficulty was experienced in making thoroughly even yarn, owing to the fact that efficient supervision could not be obtained from the operatives superintending the prepara tory processes. It will be clear that when six, eight, or other numbers of slivers are drawn together iuto one, should one or more of these become exhausted or broken, and the draught of the remainder continue, the resulting sliver will be proportionately reduced in substance and strength. Wherever two or more threads are worked together to form one, this is liable t,o occur, and, when it happens, the commercial product is seriously depreciated in value. These defects were constantly pressed upon the notice of the trade, and led to many attempts at their removal ; but success was not obtained until James Smith, of Deanston, invented the above-described stop motion, which partially remedied the evil. Since bis day it has been considerably improved, but, at its best, has hitherto left much to be desired. It will be obvious, from the description, that its sensitiveness and constant action are dependent upon the presence of conditions which cannot always be assured. 1Vlany attempts to further improve it have been made, but without much success. It is, however, likely to be superseded by the electric stop motion, recently introduced by Howard and Bullough, of Accrington.
The inventors of this novel improvement, having regard to the fact that mechanical stop motions as ordinarily constructed are often either too cumbrous or c,omplex to be sufficiently sensitive, or, if the latter be attained, are too fragile in their parts to be durable, sought to reduce these to a mini mum, and, if possible, to increase the sensitivity. The idea of employing electricity for this purpose suggested itself, and the fact that c,otton wool, iu its ordinary c,ondition of dryness, is a non-conductor, favoured the plan. After considerable effort, the iuvention was perfected ; and, in practical appli cation, it has been found to be all that could be desired.
To supply the electric current, the inventors employ a small magoeto-electric machine, which is driven by a band or belt from the shafting that drives the machinery. It is very Mall, and the power needed is not more than would suffice to drive a small domestic sewing machine.
In Fig. 540 is seen a section of the chief working parts of the drawiog-frame, with sufficient detail to show the application of tbe electric stop motion. The rods 17 and T convey electiicity from the generating machine to the frame. The parts marked A, C, D, E, sre connected with T, and H, K, L, N, with V. The drawing-frame requires to be stopped on any of the following oc,currences :--on the breakage of the sliver M at any part, or on the exhaustion of the 'supply ; on its lapping around the front rollers ; and on the can Z becoming full. The insertion of the sliver between the rollers pre
vents electrical contact taking place. Should breakage occur, the slight space is instantly closed, the electric circuit is com pleted, and the small magnet P ls endowed with power to attract the lever, which stops the revolving notched shaft S ; this, by means of a catch box, as in the ordinary stop motion, moves the driving strap from the fast to the loose pulley. Should the sliver, or a part of it, begin to lap round either of the front rollers, the space be tween them is increased, the top roller K rising soon comes into contact with the screw C, which completes the elec tric circuit again, and stops the machine. When the can Z is filled, and the sliver would run to waste if not attended to, its accumulation lifts the tube wheel N, until it comes into contact with the point E, when electrical contact again takes place, and tbe machine is stopped. By means of another arrangement, the electrical circuit is broken when the machine stops, and the force is made available for the needs of other machinery.
The introduction and utilization of this subtle agent iu a realm of industry which is almost exclusively occupied by mechanical powers is quite new, and, in the cases of the drawing, slubbing, and intermediate roving-frames, to which it has been applied, has proved highly satisfactory. For the carding-engine, and the final roving-frame, to which it has also been applied,-the invent,ors do not so strongly recommend it ; but in neither of these cases is it so necessary, as the purposes to be answered, and the difficulties to be obviated, are not so important.
In the drawing process, the number of times the material should be doubled and dmwn is chiefly dependent upon the class of cotton used. The object being to draw the fibres into parallel positions with regard to each other, drawing, carried beyond the point at which this is accomplished, is in jurious and wasteful, weakening the fibre, and entailing loss. The varieties of cotton in which the fibre is soft and pliable, such as American qualities, brown Egyptian, and soft Peruvian, require less doubling than the harsh and intractable descriptions, such as Brazilians, itc. Much also in practice depends upon personal opinions. For the softer descriptions, when intended for yarns not exceeding 30's or 32's, putting it through two heads of eight ends each, thus doubling sixty-four times, will generally be found sufficient. In other mixings, or when higher numbers are spun, the employment of three heads of drawings is necessary ; one of eight, and two of six ends each, being equal to 288 doublings. Sometimes eight ends are put through each head, when the number becomes 512.