296 REPORT OF NATIONAL MUSEUM, 1899. 



from 1| by 2 inches up to 8 by 10 inches, the prices ranging from 40 

 cents to $13 a pound. For electrical work upward of 400 patterns 

 are called for, the prices varying from 10 cents to $2.50 a pound. 



3. ASBESTOS. 



The name asbestos in its original sense includes only a fibrous variety 

 of the mineral amphibole; hence is a normal metasilicate of calcium 

 and magnesium with usually varying amounts of iron and manga- 

 nese and not infrequently smaller quantities of the alkalies. As is 

 well known, the amphiboles crystallize in the monoclinic system in 

 forms varying from short, stout crystals, like common hornblende, to 

 long columnar or even fibrous forms, to which the names actinolite, 

 tremolite, and asbestos are applied. The word asbestos is derived 

 from the Greek afffifffros, signifying incombustible, in allusion to its 

 fireproof qualities. The name "amianthus" was given it by the 

 Greeks and Romans, the word signifying undefiled, and was applied in 

 allusion to the fact that cloth made from it could be readily cleansed 

 by throwing it into the fire. As now used, this term is properly 

 limited to fibrous varieties of serpentine. Owing to careless usage, and 

 in part to ignorance, the name asbestos 1 is now applied to at least four 

 distinct minerals, having in common only a fibrous structure and more 

 or less fire and acid proof properties. These four minerals are: First, 

 true asbestos; second, anthophyllite; third, fibrous serpentine (chryso- 

 tile), and, fourth, crocidolite. The true asbestos is of a white or gray 

 color, sometimes greenish or stained yellowish by iron oxide. Its 

 fibrous structure is, however, its most marked characteristic, the entire 

 mass of material as taken from the ledge or mine being susceptible of 

 being shredded up into fine fibers sometimes several feet in length. In 

 the better varieties the fibers are sufficiently elastic to permit of their 

 being woven into cloth. Often, however, through the effect of 

 weathering or other agencies, the fibers are brittle and suitable only 

 for felts and other nonconducting materials. The shape of an asbestos 

 fiber is as a rule polygonal in outline and of a quite uniform diameter, 

 as shown in the illustration (fig. 10); often, however, the fibers are 

 splinter like, running into fine, needle-like points at the extremity. 

 The diameters of these fibers is quite variable, and, indeed, in many 

 instances there seems no practical limit to the shredding. Down to a 

 diameter of 0.002 mm. and sometimes to even 0.001 mm. the fibers 

 retain their uniform diameter and polygonal outlines. Beyond this, 

 however, they become splinter like and irregular as above noted. 



The mineral anthophyllite like amphibole occurs in both massive, 

 platy, and fibrous forms, the fibrous form being to the unaided eye 

 indistinguishable from the true asbestos. 



1 Also spelled asbestus. The termination o seems most desirable when the deriva- 

 tion of the word is considered. 



