This section is from "Scientific American Supplement". Also available from Amazon: Scientific American Reference Book.
[Table referred to in a paper read before the Birmingham Photographic Society by G.M. JONES, M.P.S.]
SUBSTANCE. | IMPURITIES POSSIBLY PRESENT. | TESTS. |
---|---|---|
Ammonia, NH Molec. Wt. 17 | Carbonic acid | Renders lime-water milky. |
Dissolved solid matter | Residue left on evaporation. | |
Chlorides | After acidulating with nitric acid, it gives a precipitate with silver nitrate, which after washing is readily soluble in ammonia and reprecipitated by nitric acid. | |
Sulphates | After acidulating with nitric acid, it gives a precipitate with barium nitrate. | |
Lime | A white precipitate with oxalate of ammonium. | |
Lead is often present, derived from the action upon flint glass bottles | Black precipitate with sulphureted hydrogen. | |
Nitric acid, H, NO Molec. Wt. 63 | Traces of sulphuric acid | After dilution it gives a precipitate with barium nitrate. |
Chlorides | After dilution it gives a precipitate with silver nitrate. | |
Peroxide of nitrogen | The acid is yellow. | |
Iodine may be present if the acid be prepared from sodium nitrate. | After dilution and cooling it gives a blue color with starch, paste, or mucilage. | |
Hydrochloric acid, HCl Molec. Wt. 36.5 | Free chlorine | Liberates iodine from solution of potassium iodide. See also "Chlorides," nitric acid. |
Sulphuric acid | As above for nitric acid. | |
Perchloride of iron | Yellow color. Brown precipitate with ammonia added till it smells slightly. | |
Sulphuric acid, HSO Molec. Wt. 98 | Bisulphate of potassium | Residue on evaporation. |
Sulphate of lead | Milkiness on dilution. May be completely freed from lead by diluting with three or four times as much water, and allowing to settle. | |
Acetic acid (glacial), H CHO Molec. Wt. 60 | Water | Does not solidify when cooled to 17° C. (53º F.) |
Sulphurous and hydrochloric acids | White precipitates with silver nitrate. | |
Aldehyde, or volatile tarry matter | Blackens in the light after adding silver nitrate. | |
Organic sulphuric acid | Smell of garlic. | |
Citric acid, HC HOHO Molec. Wt. 210 | Tartaric acid | Strong solution of potassium. Acetate added to a strong solution of the acid will deposit white crystalline bitartrate. |
Pyrogallic acid, (CH)HO Molec. Wt. 126 | Metagallic acid | Black residue, insoluble in water. |
Silver nitrate, AgNO Molec. Wt. 170 | Free nitric acid | Reddens litmus paper. (Neutral silver nitrate does not affect litmus.) |
Potassium carbonate, KCO Molec. Wt. 138 | Chlorides and sulphates | Same as for ammonia. |
Potassium iodide, KI Molec. Wt. 166 | Potassium carbonate | A strong solution is alkaline to test paper. |
Sulphates and chlorides | Same as for ammonia. | |
Potassium iodate | A pretty strong solution becomes yellow from liberation of iodine on addition of dilute sulphuric acid or, better, a strong solution of citric acid. | |
Potassium bromide, KBr Molec. Wt. 119 | Similar to potassium iodide | See potassium iodide. |
Sodium carbonate, NaCO Molec. Wt. 106 | Chlorides and sulphates | Same as for ammonia. |
Sodium chloride, NaCl Molec. Wt. 58.5 | Chloride of calcium Chloride of magnesium | Oxalate of ammonium (after addition of a little acetic acid) gives a milkiness, or precipitate, indicating calcium; filter this out and add ammonia, chloride of ammonium, and phosphate of sodium (clear solutions). A precipitate indicates magnesium. Both the above cause dampness in wet weather. |
Sodium sulphate | As for "sulphates" in ammonia. | |
Potassium cyanide, KCN Molec. Wt. 65, and hydrate, KHO Molec. Wt. 56 | Potassium carbonate nearly always present | Effervescence with dilute acids, giving off a gas carbonic anhydride, which renders lime-water turbid. |
Kaolin | Chalk | Effervescence with dilute acids. |
Water, HO Molec. Wt. 18 | Sulphates and chlorides | Same as for ammonia. |
Calcium carbonate, temporary hardness | Deposited by boiling. Test as for calcium chloride. See sodium chloride. | |
Ammonia, almost always present in distilled and rain water | Brown coloration, or precipitate with Nessler's reagent. | |
Gelatine | Alum | Ash, sometimes as much as ten per cent. |
Fatty matter | Separated by precipitation with alcohol. Dissolved out by ether or benzine, and left as a residue on evaporation of the solvent. | |
Ammonium bromide (NH)Br Molec. Wt. 98 | Potassium bromide or other non-volatile bodies | Leaves a residue when heated. |
Ammonium chloride | Same as for chlorides in ammonia. | |
Pyrogallic acid | Powdered glass | Left behind on solution. |
Potassium iodide | Potassium bromide | The crystals of bromide are usually more transparent than those of iodide, but no reliance can be placed on this. |
Silver nitrate | Potassium nitrate, sometimes present in the fused sticks - not in the crystals | Will not yield the full quantity of chloride on precipitation with HCl. Gives a purple color to flame. |
Sulphuric acid | When vended as pure, it invariably contains a trace of iron. Common acid is also liable to contain arsenic, selenium, thalium, and many other substances. | No easy test can be given, as the substances are so numerous some of them volatile, and most require separation from the acid before detection. |
Organic matter, as a piece of straw in a carboy of acid | Gives a brown color to the acid. | |
Hydrochloric acid | Arsenic | Marsh's test. |
Some yellow samples contain no iron, but an organic salt, and give an alkaline ash on ignition of the residue after evaporation | Reinsh's test; a small piece of copper foil becomes coated on boiling in dilute acid. | |
Calcium chloride | Calcium hydrate | The clear filtered solution made with distilled water is alkaline to test paper, and gives a precipitate on breathing into it through a tube. |
Pure (?) chemicals generally | Broken glass, bits of straw, wood, paper, etc. | These impurities either float or sink on solution, and may easily be seen. |
G.M. JONES, M.P.S.
 
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