254 ANNUAL OF SCIENTIFIC DISCOVERY. 



ing the strain which Preller's leather of ^ of an inch in thickness will 

 resist in constant working. A strip of it a yard long, about half an 

 inch in width, and ^ of an inch thick, gave way with a breaking 

 weight of 6 cwts. 20 Ibs., while oxhide, well tanned on the oak-bark 

 system, and of the same dimensions, could only resist a strain 

 of 5 cwts. 



As this leather combines strength with thinness, and also with light- 

 ness, it is eminently adapted for driving bands. Its superior thinness and 

 flexibility, enables it to be passed round pulleys of only a few inches 

 in diameter ; in which service it will continue effective for a consider- 

 able time. When thick leather is employed for a similar purpose, the 

 fibers of its running surface are compressed, and those of its outer 

 surface extended, within the limits of the extreme points of contact; 

 and the rapid change of state from the normal to the extended, soon 

 exhibits itself in cracks and fissures, which are a source of loss of 

 power, and vitiate the tension originally intended. The thinness of 

 Preller's bands obviates this state of things ; as the whole of the 

 leather more nearly corresponds in its condition to that of the neutral 

 line. The bands which consist of only one thickness of leather, are 

 formed by simply cementing the ends of successive lengths, which 

 have previously been thinned away to an edge by the knife. In this 

 chamfering process the fibers crop out in abundance, and when the 

 two surfaces are brought into close contact, with a layer of cement be- 

 tween them, the fibe-rs on opposite sides embrace each other firmly, 

 and give enormous strength to the band. Compound bands, for heavy 

 work, are made by using two, three, and sometimes four thicknesses 

 of ox-hide, which are united by countersunk stitches. In either case 

 the motion is perfectly smooth not the slightest jerking action being 

 propagated throughout the mechanism a result of the greatest 

 value. 



A very considerable saving of time in the process of making, is 

 another important feature incidental to this invention. Calf-skin 

 can be prepared in this manner in about twice eight hours, the 

 time consumed in agitating it twice in the drums. A short interval 

 is allowed to elapse between the two operations, but the action of the 

 converting substance is not then continued. The thickest ox-hide re- 

 quires only two days and a half to be fully converted by the applica- 

 tion of this process. Under the most favorable circumstances, it now 

 requires four or five weeks subjection to the tanning liquor. Under 

 the old process of tanning, in which the hides were placed in the pit, 

 with layers of tan to separate them, and afterwards filled with water, 

 a very considerable period has been known to elapse during the pro- 

 cess ; sometimes amounting to four years. This old-fashioned method 

 has not been yet completely abandoned for more scientific ones, and 

 contrasted with it the great change which this invention has effected 

 is the more remarkable. 



When ordinary leather is boiled in water, it gradually hardens and 

 becomes rigid ; and if the operation be continued for half an hour, it 

 will be found to have assumed a kind of woody texture, and to have 



