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44. Sodium Metaborate Dihydrate, NaB0,.2H,O (2)
.
- ,
-.
. ..
.. .
.
Formuis Tcight. 101.$1. Density. 1,905 (Rotat,ion :tud dm+ii,yI~B~W.IICP); 1.909 * O.OOG(1).
.
.
1.80 (x-ray).,
O P T I C I I . PROPERTIES
Refractive Indexes (58!Yd -4.; 2.5' C.1. a = 1.439 + 0.002 E p = 1.43 * 0,002 y 8'. y = 1.4% * 0.002 Y y ' . p =
I diiil i1 )
'HE: dihydrate of sodium metabovate is the stable hydrat,t, ut roim temperature (1). It can be recrystallized on a miero-
Ilispersioii. T > 11, strong. Optic Axial PIanc. Appmximatdy I010. Sierr of Doublc Refraction. Seestivc. i\l;tc Riscitrix. a. Extinotion. a' A e = 43" in obtufie 8 ; a" A e = 4" in aeutr a (Figure 2). \loloaul:~r Refraction ( R ) (5893 A,; 25" C.). = l.4iiB * 0.002. nzvtrnye= 1.477 (caleulnted from (rladstonc and Dale formula). R (calcd.) = 30.2. IZ (obwd.) = 29.6.
scope slide from atrang aqueous sodium hydroxide solutions as needles and tablets (Figure 1). Sodium metaborate dihydrate is slmost monoclinic, with both a and y almost exactly 90". The orthographic projection (Figure 2) is drawn to emphasize t,he relat,ionship to the corresponding monoclinic form.
~
;/A$;
CRYSTAL MORPHOLOGY
Crvstal System. Triclinic Triclinic. Crystal Svstem. Form F o h and Habit. Needles and tablets (lying on 010) showing forms (011) ?nd and 1100) andoccasionally (001)and [ l l l ) . Axial Ratio. a : b : e = 0.641:1:0.556. a : b : c = 0.5573:l: 0.6421 (1 (1). ). Interfacial Angles (Polar). oiinoii = 50"; OIOAOII = m "v . Crystal Angles. a = 91.5"; p = 122.5"; y = 89". a = 01". 8 = 57"; y = 91.5"(1). deavaee. Excellent: oarallrl to 010 and 100. X-RAYD?FFMCTIOND i ~ i ~ Cell Dimensions. a = 6.78 A,; b = 10.58 A,; c = 5.88 A. n = 5.86A.; b = 10.51A.; e = 6.75.k. (1). Formula Wcights pcr Cell. 4.
C
C
Principal Lines d 5.71
5.29 5.03 4.48 3.80 3.63 2.91 2.87 2.75 2.64 2.51 2.42 2.33 2.29 2.24 2.21
I/II 0.04 1.00 0.60 0.12 0.61 Very weak 0.24 0.60 0.34 0.30 0.51 0.42 0.25
Very weak 0.23
0.16
2.16
0.13
2.13
0.00
d
1/11
2,008
0.15
1.980
0.16
1.935 1.901 1.872 1.849
0.20 Very weak 0.07
1.805 1.787 1,767 1.732 1.707 1.6% 1.655 1.634 1.608 1.579 1.543 1.509
0.18 0.10 0.04 0.06
Very weak 0.09 0.17
very weal. 0.13 0.14
very weak 0.06 0.05
FUSION DATA. Sodium metaborate dihydrate has an equilibrium transition tem-perature of 54" C. with NaB01.0.5H*0
ou& -portions a? the crystals toward the inner partFous of the
cryystals m a t with t h i evolution of gases a t a h o ~ t ~ i 3 C. 0 ' E&tually an amorphous and extremely viscous mas8 is obtained, which soon sets to an amorphous sodium borate glass ACKNOWLEDGMENT
It is a pleasure to acknowledge the assistance of Irene Corvin in the determination of the powder x-ray spacings and intensities. LITERATURE CITED ( I ) M e n d . H., and Sohuln, H.. 2. a n o ~ o .a l l g a . Chm.. 251, 167200 (1943). ( 2 ) Yves, Douoet, and Rollin. M.. Compt. rend., 226, 1967-8 (1948).
Figure 1. Crystals of Sodium Metaborate Dihydrate
C o ~ ~ n r ~ o ~ rofo lcryatallographio rs data for this section should be sent to Walter C. MoCrone, Anslytical Section, Ammour Research Foundation of Illinois Institute of Teelinology. Chicago 16. Ill.
Tablet and needles fzom a q u e o u s sodium hydroxide, croesed Niools
806
