522 



MACHINES, WORK, AND ENERGY 



defects. The sewing machine did not seriously affect Ameri- 

 can life until after the middle of the 19th century. About 

 1850 really practical machines were invented. Even these 



machines were crude compared with 

 the machines of today (Fig. 323). 

 618. Classes of Sewing Ma- 

 chines. Sewing machines may be 

 classified according to the kind of 

 stitch they make. Although a 

 great variety of stitches have been 

 used at different times some 75 

 in number practically only three 

 kinds of stitches are today in use. 

 They are the LOCK STITCH, the 

 CHAIN STITCH, and the BUTTON- 

 HOLE STITCH. The lock stitch is 

 the most common and, for most 

 purposes, the most satisfactory. 

 Chain-stitch machines, however, 

 have advantages for certain pur- 

 poses : 



1. Chain-stitch machines are simpler in construction and 

 generally use but a single thread. 2. The thread, when 

 sewed into a seam, is readily removed, i.e., the seam is quickly 

 ripped out by the mere breaking of the thread. 3. The seam 

 sewed by means of the chain stitch is elastic, while the lock- 

 stitch seam is not. 4. The chain-stitch machine can be oper- 

 ated satisfactorily at a higher speed than the lock-stitch 

 machine. Figure 324 shows the manner in which the chain- 

 stitch machine forms the stitch. 



Chain-stitch machines are frequently used in factories pro- 

 ducing ready-made garments on account of their greater speed. 

 Owing to the ease with which a chain-stitch seam may be 

 ripped, and the liability of a stitch's being broken by accident, 

 the chain-stitch seam is not regarded as satisfactory for many 

 purposes. 



FIG. 323. Sewing machine, 

 1850. The shipping box was 

 used as a table for the machine. 



