CORK, ITS MANUFACTURE AND PROPERTIES. 637 



winds and insolations, has the additional advantage of expediting by 

 a year the time when the next crop of cork will be fit to gather in. 



Before being put into the market, the bark has to be subjected to 

 the operations of steeping, scraping, sorting, and packing. The object 

 of the steeping, which is performed in large boilers of water, heated 

 by means of chips of the bark, is to swell the cork and increase its 

 elasticity, and it has the further effect of enabling curved pieces to be 

 made straight. Scraping, for the removal of the woody parts, is done 

 with iron scrapers, or with a machine in which the rotating chisels 

 make nine hundred turns in a minute. It involves a loss of twenty- 

 eight per cent of the crude bark, but is not so necessary when the 

 formation of the young cork has been protected in the manner that 

 we have described. In England, these two primary operations are re- 

 placed by a process of scorching and brushing the bark. The sorting 

 is done with reference to five degrees of thickness, after which the 

 bark is packed in bales containing about two hundred pounds each. 

 At the market it undergoes another testing for quality, in which there 

 is a wide range, and a corresponding diversity of prices. According 

 to M. Lamey, in his book on " The Cork-Oak in Algeria," the bark 

 should never be gathered till it is seven eighths of an inch thick, and 

 that is preferred in commerce which is from one and an eighth to 

 one and a quarter inch thick. To produce such thickness, from six to 

 nine years of growth are needed. 



The density of cork varies with its quality and age. Thin corks 

 are usually heavier than those of the same volume that have grown 

 more rapidly, and, in corks of the same class, the density increases 

 with the age. M. Brisson gives 0*240 as an average maximum, and 

 the ordinary density of a ten-years-old cork may be taken at 02. 

 With extreme lightness are associated other valuable qualities : that 

 of being a poor conductor of heat and sound ; impermeability to 

 liquids ; imperfect combustibility, and non-liability to decay, by reason 

 of which it is susceptible of very numerous applications in industry. 

 The most important use of the substance is for bottle-corks. The bark 

 which is intended to be used in this form is kept in a damp cellar. 

 When taken to the shop, it is cut by the first workman into strips, the 

 width of which corresponds with the length of the future cork. A 

 second workman cuts these strips into squares suited in size to its 

 diameter. The squares, strung, are plunged into boiling water to 

 make them swell out. They are then stored in a cool place, and kept 

 constantly moist by sprinkling, till they pass into the hands of the 

 cork-maker. He applies them in succession, giving them a rotary 

 motion, to the edge of a wide-bladed knife, drawing them at the same 

 time slowly along its length, and by skillful manipulation transforms 

 the square into a round cork. This is the method usually practiced in 

 France. Workmen in other countries handle the knife in different 

 manners. It is essential, to obtain a good and solid cork, to take care 



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