206 BULLETIN 42, UNITED STATES NATIONAL MUSEUM. 



Emery stone. 



(\) To be ground and glued on to the paper; from Turkey. Two specimens. 

 (5.')242.) 

 Ground, ready to be glued ou to the paper : 



(2) Size 00. (55245.) 



(3) Size 0. (55246.) 



(4) Sizei. (55247.) 



(5) Size 1. (55248.) 



(6) SizeU. (55249.) 



(7) Size 2. (55250.) 



(8) Size2i. (55251.) 



(9) Size 3. (55252.) 



An average sample of these sizes, analyzed in the laboratory of the Department, 

 by Mr. J. A. Allen, gave — 



Pur cent. 



Water (H2O) .3.60 



Silica(Si02) 10.69 



Alumina (AI.2O3) 58.98 



Titanic acid(Ti0.2) ; 2.79 



Sesquioxide of iron (FcaOa) 10.57 



Protoxide of iron (FeO) 11.89 



Oxide of manganese (MnO) 0.32 



Lime (CaO) 0.91 



Magnesia (MgO) 0.63 



100. 38 



(1) Emery paper, a roll as made and ready to be cut in to sheets ; the emery has 

 been fastened ou to the mauilla paper by the glue. (55261.) 



(2) Emery paper, a series of eight sheets, showing the different sizes of ground 

 emery used. The sheets are one-fourth the regular size. (55263.) 



ASBESTOS. 



Asbestos is a natural mineral fiber, incombustible and infusible at 

 ordinary high temperatures. It finds wide application where resistance 

 to high temperature is required. There are three minerals which oc- 

 cur in a fibrous form possessing the required characters ; these are pyr- 

 oxene, hornblende, and serpentine. Pyroxene and hornblende are 

 essentially of the same chemical composition, being complex anhydrous 

 bisilicates, containing alumina, iron, and magnesia. The fibrous varieties, 

 however, generally contain little or no alumina, the average composi- 

 tion being, about, silica 55 per cent., protoxide of iron 12 percent., and 

 magnesia from 26 to 30 per cent. 



It is very difficult, and in many cases impossible, to distinguish be- 

 tween pyroxene and hornblende in the fibrous state, since the difference 

 between the two minerals is mainly in the habit of crystallization, and 

 this is not shown by the fibers. It is only by association that they can 

 be distinguished. In the collection no attempt has been made to sepa- 

 rate the two minerals, since the specimens are entirely removed from 

 all their associates. Hornblende is much more common in the fibrous 

 form, and this name has been given to all the specimens except the 

 serpentine. 



Serpentine is ahydrated uuisilicate of magnesia, containing silica 43.5 



