4i8 JOSEPH STRUTHERS 



crystals of boric acid are obtained by evaporating the solution. 



Several forms of borax are used in industrial, medicinal, 

 and laboratory processes — the principal one being prismatic 

 sodium borate (borax, Na3B4O7.10H2O). There is a second 

 variety called octahedral borax which contains five molecules 

 of water of crystalhzation (Na3B407.5H30), forming octahedral 

 crystals. The latter variety, unlike prismatic borax, becomes 

 opaque upon exposure to moist air and is converted by the ab- 

 sorption of water into the prismatic form. 



A property of molten borax of great utility in analytical 

 research is that of dissolving various metalhc oxides, thereby 

 forming transparent glasses of characteristic colors. By mak- 

 ing a borax bead on a loop of platinum wire held in a blowpipe 

 flame, and dissolving therein the substance under examination, 

 the presence of certain metals is easily distinguished. 



Borax is also of great value in assaying gold and silver 

 ores, being used to dissolve and remove the base metals from 

 the metallic lead button containing the gold and silver of the 

 sample of ore tested. This property of dissolving oxides is 

 utihzed also in soldering and brazing metals that are oxidizable 

 by heat; the molten borax absorbing any oxides formed whose 

 presence mechanically would prevent the close adhesion of the 

 metals so necessary for a proper weld or soldered joint. 



Among other important uses are as a constituent of strass 

 or paste for making glass and enamels; as a glaze for fine 

 earthenware; in combination with shellac as a varnish for 

 stiffening felt hats ; with casein as a substitute for gum arable, 

 and (on account of its antiseptic qualities) as a household soap ; 

 as an ingredient of various cosmetics. 



Boric acid (H3BO3) (old name boracic acid) : In Tuscany 

 the vapors escaping from the hot springs and from openings in 

 the ground (fumaroles) contain boric acid, and in some places 

 this substance is obtained as crystals by the evaporation of 

 water from there fumaroles. The crystals or crusts produced 

 naturally form the mineral sassolite. The crystals of boric acid 

 are white in color, laminated in structure, and possess a mother- 

 of-pearl luster. They dissolve readily in hot water though 

 very shghtly in cold. Upon being heated to 160° C. they lose 



