Organic matter contains also minerals which can be detected. By incineration of dry substance the organogenic elements escape in form of CO₂, H₂O , H₂S and NH₃.
As ash remain carbonates and oxides. The following ions can be detected:
Na⁺, K⁺, Ca²⁺, Fe³⁺, S^2-, SO₄^2-, CO₃^2-, HPO₄^2-, Cl^-

E.g. the ash of tobacco leaves contains:
29,1% K₂O, 3,2% Na₂O, 36% CaO, 7,4% MgO, 1,9% Fe₂O₃, 4,7% P₂O₅,
3,1% SO₃, 5,8% SiO₂, 6,7% Cl^-

For the following experiments you need half a test-tube of cigarette ash!

Flame tests

With a small part of the substance do the flame test as you learned before. Let the teacher explain how to detect sodium and potassium together by using a cobalt glass!

Detection of water-soluble components

A test-tube is filled to a quarter with ash and then half filled with aqua dest.
Shake well! - After filtration the following two ions can be detected:
Sulfate: Take half of the filtrate and add a small amount of dil. HCl followed by a few drops of BaCl₂-solution. A white ppt. indicates sulfate.
Chloride: Add to the other half of the filtrate a small amount of dil. HNO₃ followed by a few drops of silver nitrate-solution. A white ppt. soluble in excess ammonia indicates chloride


Detection of components soluble in acidic medium

Carbonate and sulfide

Fill a test-tube to 1/4 with ash. Prepare a pass-over glass by filling it with baryta water and connecting it with a bore through-stopper.
Add a small amount of dil.HCl and immediately close it with the prepared glass and stopper. A white ppt. in the baryta water indicates carbonate.

After this the stopper is removed and the t.-t. heated. Hold a lead acetate-paper at the opening. A brown-metallic coloration indicates sulfide.

Now fill the t.-t. half with del. HCl and warm until no more gas formation can be observed. Filter and divide the filtrate into 3 new test-tubes.

Phosphate: Add a small amount of conc. HNO₃ to filtrate 1 and a small amount of Ammoniummolybdate-solution. A yellow ppt. after warming indicates phosphate.

Ferric ions: Add a few drops of KSCN-solution to filtrate 2. A deep red colour indicates Fe³⁺ (Formation of Fe(SCN)₃)

Ca²⁺-ions: Make filtrate 3 basic by addition of del. NaOH. Hereby a ppt. is formed.
By addition of dil. acetic acid together with solid sodium acetate most of the ppt. dissolves. The condition must be weak acidic!
Filter and add to the filtrate ammoniumoxalate-solution. A white ppt.indicates Ca²⁺ (Formation of Ca(C₂O₄))

Try to detect the ions above in liquid fertilizer for plants!

Additional step before analysis of anions in solutions

Many of the special tests mentioned above can be disturbed by presence of heavy metal cations. Therefore you have to remove them before you make special tests. Heavy metal cations form insoluble ppts. with carbonate ions and can be removed by addition of carbonate.

Procedure:
Fill a quarter of a test-tube with the fertilizer solution and add three spatula of
anhydrous soda (sodium carbonate). Boil carefully for ca. 1 minute and filter or centrifuge. As long as the filtrate is coloured still there are heavy metal cations
present. So evtl. you have to repeat that procedure.
With the clear and colourless filtrate you can do all the tests described above. Acidify carefully because CO₂ will evaporate and check with pH-paper until the solution is acidic.
Of course the carbonate test must be done with the original solution before carbonate is added!