248 
ELEMENTARY CHEMICAL MICROSCOPY 
Table VI. 
REFRACTIVE INDICES AND CHARACTER OF DOUBLE 
REFRACTION OF TYPICAL CRYSTALS. 
Name. 
Formula. 
Crystal 
system 
Refractive index 
”d- 
Double 
refrac¬ 
tion. 
a or CO. 
|8 or e. 
7 - 
Ammonium nickel sulphate.... 
(NH4)2 Ni (SO.), • 6 H2O 
M 
1.489 
1.498 
1.508 
+ 
Ammonium o.xalate. 
(NH 4 ) 2 C 204 - H2O 
0 
1.438 
1.547 
1.595 
— 
Ammonium persulphate. 
(NH 4 ) 2 S 208 
M 
1.498 
I . 502 
1.587 
+ 
Barium chloride. 
BaCb • 2 H2O 
M 
1.635 
1.646 
1.660 
+ 
Copper sulphate. 
CUSO4 • 5 HjO 
Tr 
1.514 
1.536 
1.543 
+ 
Magnesium sulphate. 
MgS04 • 7 H2O 
0 
1.432 
1.455 
1.461 
— 
Mercuric chloride. 
HgCl2 
0 
1.74 
1.71 
1.72 
— 
Mercuric cyanide. 
Hg(CN)2 
T 
1.6s 
I 60 
— 
Potassium antimonyl tartrate.. 
K (Sb 0 )C 4 H 40 ,-H 20 
0 
1.619 
1.636 
1.637 
— 
Potassium arsenate. 
H2KASO4 
T 
I .57 
1.52 
— 
Potassium bichromate. 
IC 2 Cr 207 
Tr 
1.72 
1.74 
1.82 
+ 
Potassium nickel sulphate. 
KjNi (S 04)2 • 6 H2O 
M 
1.484 
1.492 
1.505 
+ 
Potassium nitrate. 
KNO3 
0 
I 335 
1.505 
1.506 
— 
Potassium persulphate. 
K2S20g 
Tr 
1.461 
1.467 
1.566 
+ 
Potassium sulphate. 
K2S04 
0 
1.493 
1.494 
1.498 
+ 
Silver nitrate. 
AgNOs 
0 
1.729 
1.788 
+ 
Sodium borate (tetra). 
Na2B407 • 10H2O 
M 
1.446 
1.469 
1.472 
— 
Sodium nitrate. 
NaNOs 
H 
1.58 
1.33 
— 
Sodium phosphate (tertiary).... 
Na3P04 • 12 H2O 
H 
1.44 
1.45 
+ 
Sodium phosphate (secondary). 
HNa2P04 • 12H2O 
M 
1.4,32 
1.436 
1.437 
— 
Sodium thiosulphate. 
Na2S203 • 5 H2O 
M 
1.488 
1.508 
1.536 
+ 
Strontium antimonyl tartrate.. 
Sr(Sb 0 ) 2 (C 4 H 406)2 
H 
1.638 
1.587 
— 
Sucrose. 
C12H22011 
M 
1.538 
1.566 
1.571 
— 
Tartaric acid. 
H2C4H40, 
M 
1.583 
1.566 
1.571 
+ 
Urea. 
CO (NH2)2 
T 
1.485 
I. 61 
+ 
Zinc sulphate. 
ZnS04 • 7 H2O 
0 
1.46 
1.48 
1.49 
* Values for n have been taken from Groth’s tables and checked in the laboratory. For uni¬ 
axial crystals the first column is « and the second e. For biaxial crystals the first column is a, 
the second /3 and the third 7. 
REFERENCES. 
Tables of refractive indices in the following articles will be found by the analyst 
of great value in the identification of compounds by means of the immersion 
method. 
Schroeder van der Kolk — Tabellen zur mikroskopischen Bestimmung der 
Mineralien nach ihren Brechnungsindex, Zeit. anal. Chem., 38 (1899), 615. 
Kley — Ein Beitrag zur Analyse der Alkaloide, Zeit. anal. Chem., 43 (1904), 160. 
Bolland — Die Brechnungs indices der weinsauren Alkaloide nach Einbettungs- 
methode. Monats., 29 (1908), 991. Die Brechnungsindices krystallinischer- 
chemischer Individuen nach der Einbettungsmethode von Standpunkte der ana- 
lytischen Praxis. Monats., 31 (1910), 387. 
