428 
ELEMENTARY CHEMICAL MICROSCOPY 
needles or prisms of calcium sulphate results. See Calcium, 
page 334. 
h. To the drop add a trace of Potassium Chromate, a trace of 
Nitric Acid and a drop of Silver Nitrate. Characteristic crystals 
of silver sulphate will be obtained, stained yellow through solid 
solution of the silver chromate. See Silver, page 381. 
SULPHITES, THIOSULPHATES. 
а. To a drop of a solution of potassium iodate add a little 
potato starch and a small drop of dilute sulphuric acid. Ex¬ 
amine to see that no iodine has been set free. Add a fragment 
of the unknown. The starch is colored blue. 
б. To a moderately concentrated drop of copper sulphate 
apply a drop of a solution of the unknown by Method III A, 
page 302. Warm gently — sulphites, if pure and undecom¬ 
posed, yield at the most only a faint cloudiness — thiosul¬ 
phates give a brown precipitate of copper sulphide and around 
the circumference of the drop lemon-yellow crystals of copper 
thiosulphate. 
SULPHIDES. 
a. The Silver Nitrate Precipitate was Black. 
h. Place a drop of solution or fragment of solid in the distilling 
apparatus, cover with a slide holding a tiny drop of silver nitrate 
and one of lead acetate side by side. Raise the cover and care¬ 
fully run in a drop or two of dilute hydrochloric acid. Cover 
quickly and allow to stand. Both drops turn black. 
c. Proceed exactly as in h but invert over the crucible a slide 
carrying a drop of sodium nitroprusside made alkaline with 
sodium hydroxide. A beautiful purple color results. The 
reagent drop must be alkaline with sodium or ammonium 
hydroxide. 
THIOCYANATES. 
a. Give a Blood-red Color with dilute Ferric Chloride. 
b. Add Mercuric Chloride and Zinc Sulphate. There will be 
obtained the double thiocyanate of mercury and zinc. See Zinc, 
