CAOUTCHOUC 



701 



Second machine for subdividing the ribands. Figs. 407, 408. The riband is engaged 

 between the circular knives c c, -which are mounted upon the rollers E R ; thin brass 

 washers keep these knives apart at a distance which may be varied, and two extreme 

 washers mounted with screws on each roller maintain the whole system. The axes of 

 these rollers traverse two uprights M M, furnished with brasses, and -with adjusting 

 screws to approximate them at pleasure. The axis of the lower roller carries a wheel 



407 



r 



r, which takes into another smaller -wheel r f , placed upon the same shaft as the pulley 

 p, which is driven by a cord. The diameter of the wheel r is three times greater than 

 the wheel r 1 . The pulley p is twice the size of the wheel r' ; and its cord passes round 

 a drum B, which drives the rest of the machine. 



Threads of caoutchouc are readily pieced by paring the broken ends obliquely with 

 scissors, and then pressing them together with clean fingers, taking care to admit no 

 grease or moisture within the junction-line. These threads must be deprived of their 

 elasticity before they can be made subservient to any torsile or textile manufacture. 

 Each thread is inelasticated individually in the act of reeling, by the tenter boy or 

 girl pressing it between the moist thumb and finger, so as to stretch it to at least 

 eight times its natural length, while it is drawn rapidly through between them by the 

 rotation of the power-driven wheel. This extension is accompanied with condensation 

 of the caoutchouc, and with very considerable disengagement of heat, as pointed out in 

 Nicholson's Journal upwards of 35 years ago, by Mr. Gough, the blind philosopher of 

 Kendal. To stretch the thread, in the act of reeling, the sensation of heat is too 

 painful for unseasoned fingers. The reels, after being completely filled with the 

 thread, are laid aside for some days, more or fewer, according to the quality of the 

 caoutchouc, the recomposed requiring a longer period than the bottle material. 

 When thus rendered inelastic, it is wound off upon bobbins of various sizes, adapted 

 to various sizes of braiding, or other machines, where it is to be clothed with cotton or 

 other yarn. 



In the process of making the ELASTIC TISSUES, the threads of caoutchouc being first 

 of all deprived of their elasticity, are prepared for receiving a sheath upon the 

 braiding machine. For this purpose they are stretched by hand, in the act of wind- 

 ing upon the reel, to 7 or 8 times their natural length, and left two or three weeks in 

 that state of tension upon the reels. Thread thus inelasticated has a specific gravity 

 of no less than 0'948732 ; but when it has its elasticity restored, and its length reduced 

 to its pristine state, by rubbing between the warm palms of the hands, the specific 

 gravity of the same piece of thread is reduced to 0-925939. This phenomenon is akin 

 to that exhibited in the process of wire-drawing, where the iron or brass gets condensed, 

 hard, and brittle, while it disengages much heat ; which the caoutchouc thread also 

 does in a degree intolerable to unpractised fingers. 



For the solution of India-rubber, for the manufacture of elastic tissues, the follow- 

 ing has been strongly recommended : 



The raw India-rubber is soaked in clear water, and boiled for about an hour, to 

 remove dirt. It is then taken out of the water and cut into round slices about one 

 centim. in thickness. It is then rolled out into layers about 2 metres long and 0'15 

 metre broad. The rubber is then dried in a warm chamber. After the drying follows 

 the solution. About 26 kilos of rolled caoutchouc are placed in a wooden vat, lined 

 with zinc, and treated with a mixture of 50 kilos benzol, and 70 kilos oil of turpentine. 

 Both these liquids must be perfectly free from fatty matters, or the solution of India- 

 rubber -will bo useless. The caoutchouc, before being brought into contact with the 

 solvents, is torn up into small fragments. The mass is stirred occasionally, till it forms 

 a thick, homogeneous liquid. To test the benzol and turpentine, small portions of each 

 are evaporated to dryness in the water-bath. If any trace of fat remains, the samplo 

 is at once rejected. 



