The Laundry 1109 



According to the source of the wool from which the fiber is obtained, 

 its surface is comparatively smooth or its serrated edge is very conspicuous. 

 Wool fiber has been shown to be composed of numerous small segments, 

 called cells, the overlapping edges of which give a characteristic external 

 horny layer. When woolen cloth is wet, its fibers expand somewhat and 

 there is a loosening of the projecting edges of their segments. As the 

 cloth dries, the projections of adjacent fibers interlock, drawing the fibers 

 closer together. If the cloth is dried slowly the interlocking is slight. 

 If the cloth is rubbed briskly while wet, or if a hot iron is used in ironing 

 it, the interlocking of its fibers is increased and the shrinkage is corre- 

 spondingly greater. The use of strong soap on woolen goods greatly 

 increases the amount of shrinkage ; for the alkali of the soap acts chemically 

 on the woolen fiber, softens it, and causes the toothed edges to become 

 more prominent. A marked interlocking of fibers occurs, causing the 

 characteristic decrease in the size of the garment, with the attendant 

 thickening of its fibers resulting in the board-like condition of badly- 

 washed wool. 



Action of alkalis on wool. — Strong solutions of alkali, such as lye or 

 washing soda, have a softening effect on wool; if allowed to act on it for 

 any length of time they reduce it to a soapy-like liquid. 



Dilute solutions of borax, or a mild soap, if not much hotter than blood 

 heat, have only a slightly injurious action on wool. In cleaning woolen 

 fabrics a good mild soap is the least injiuious form in which to use an 

 alkali. 



Action of acids on wool. — Dilute acid does not affect wool materials, 

 but strong mineral acids will decompose them. In no case is the action 

 of acids on wool so destructive as on cotton. Dilute acid may be dried on 

 wool with no noticeable weakening of the fiber. 



Comparative action of acids and alkalis on cotton and wool. — A graphic 

 illustration of the comparative action of acids and of alkalis on wool and 

 on cotton and linen is furnished by an experiment that may be performed 

 to determine whether a fabric is all wool, or part wool and part cotton: 



Saturate a piece of the cloth to be tested in dilute sulphuric acid. Dry 

 it without washing. Rub it briskly between the hands. If cotton is 

 present it will fall out in the form of grayish white powder. Or weigh a 

 small sample of the material and boil it for four or five minutes in a 4 per 

 cent solution of lye. Dry and weigh it again. The final weighing will 

 show how much of the material is wool, for the lost wool will have decreased 

 the weight of the piece of cloth correspondingly. 



Silk 



Silk is the most delicate of all fabrics and stands halfway between 

 cotton and wool in its reaction toward both acids and alkalis. 



