MICROCHEMICAL REACTIONS OF ARSENIC 
395 
Sb, Pb, Sn, Pt, Ir, Os, Pd, Ru. All salts of this series are iso- 
morphous (Groth). 
EXPERIMENTS. 
Test a concentrated and a dilute solution containing Sn. 
ARSENIC. 
Crystal Forms and Optical Properties of Common Salts of 
Arsenic. 
A. ISOTROPIC. — Trioxide (I, also, but rarely mono¬ 
clinic) . 
B. ANISOTROPIC. 
Hexagonal. —Triiodide; silver arsenate (second¬ 
ary, normal is I ?). 
Tetragonal. — Secondary potassium arsenate. 
Orthorhombic. — Calcium - ammonium arsenate; 
magnesium-ammonium arsenate. 
Monoclinic. — Primary ammonium arsenate; pri¬ 
mary sodium arsenate. 
Triclinic. 
DETECTION. 
A. Through the Formation of Arsine and its Reaction with a 
Crystal of Silver Nitrate. 
Use the distilling tube. Fig. 156, page 296, as a generator, 
as indicated in Figs. 161 and 162. 
Fit the side tube with a plug of soft wood P. Introduce two or 
three fragments of arsenic-free zinc Z, and through a pipette 
dilute hydrochloric acid A (the acid will not flow into the lower 
part of the tube until the plug P is loosened). Insert a loose 
plug of absorbent cotton C which has been soaked in lead acetate 
and dried. The plug P is next withdrawn. The acid is allowed 
to flow upon the pure zinc; a tiny drop of water 5 is introduced 
into the side tube and the plug reinserted. This drop makes a 
tight seal and prevents loss of gas. The tube is now tipped 
downward and a tube drawn down to a capillary and containing 
