The 1827 Christmas Lectures
of Michael Faraday

Lecture #4

Nitric Acid or Aquafortis -- Ammonia or Volatile Alkali -- Muriatic Acid or Spirit of Salt -- Chlorine

Faraday's fourth lecture includes demonstrations of the preparation and properties of two different acids (nitric and hydrochloric) and gases such as ammonia, hydrogen chloride and chlorine. He demonstrates the properties of these substances, through the use of indicators, illustrates the acid/base character of these substances and shows some of their useful properties.

Faraday opens with a discussion of aqua fortis (nitric acid). He prepares a quantity of the acid and demonstrates many of its chemical and physical properties (Exp. 1-7).

The second substance used in the demonstration is spirit of hartshorn (aqueous ammonia). He prepares and concentrates the gas by different methods (Exp. 8-10) and then shows its chemical and physical properties (Exp. 11-23). He notes its great degree of solubility in water and demonstrates characteristics of both the gas and the water solution.

Next he turns his attention to muriatic acid (hydrochloric acid) and again demonstrates a method of preparation (Exp. 24) and shows his audience many of its interesting physical and chemical characteristics (Exp. 25-33). He then demonstrates some of the reactions between an acid and the base ammonia (Exp. 34-35).

The last substance he prepares is chlorine gas. Again he gives methods of preparation (Exp. 36-37) and demonstrates chemical and physical properties (Exp. 38-44).

In this lecture Faraday is not only illustrating the characteristics of these four substances but is also demonstrating how many of them react with each other. On this day he performs 44 experiments as demonstrations. A list of what he records in his notes follows with a brief statement of what we believe he actually did.

Aqua fortis - (nitric acid)

Exp. 1: Preparation of aqua fortis

Nitre (potassium nitrate) and oil of vitriol (sulfuric acid) were heated together in a retort, the nitric acid produced was cooled and collected in a glass vessel.

Exp. 2: Effect on indicators, solubility and taste

Indicators such as litmus (blue liquor), cabbage liquor and turmeric were used. The sour taste was noted as well as the degree of solubility in water.

Exp. 3: Heating the acid

A small quantity of the acid was heated and the fumes given off were noted (presumably these were nitrogen dioxide).

Exp. 4: Action of the acid on protein materials

Nitric acid causes a color change to yellow-brown when in contact with protein-containing materials such as skin, parchment, etc. By contrast ammonia often causes such materials to turn orange.

Exp. 5: Action on metals

Metals such as copper, lead, and tin foil were ``dissolved'' in the acid solution.

Exp. 6: Action on burning objects

Charcoal was oxidized to carbon dioxide, sulfur oxidized to sulfuric acid. To illustrate this concept, Faraday used ``burning'' alcohol, turpentine and phosphorus.

Exp. 7: Reactions of charcoal and nitre, also gunpowder

Demonstrated the reaction of nitre (potassium nitrate) and charcoal resulting in the oxidation of carbon to carbon dioxide. Also used gunpowder to illustrate the oxidation of both sulfur and carbon.

Spirit of Hartshorn - (ammonia)

Exp. 8: Preparation of hartshorn from natural substances

Heated bones, hoofs, horn and other animal matter with lime to produce ammonia.

Exp. 9: Preparation of ammonia from laboratory chemicals

Heated ``mur ammonia'' (ammonium chloride) and lime (calcium oxide) to produce ammonia.

Exp. 10: Preparation of concentrated solution

A solution of ammonia was distilled to produce a more pure and a more concentrated product, i.e., ammonia gas dissolved in very little water.

Exp. 11: Method of collection of ammonia

Noting the water solubility of the gas, the method of collection was over mercury.

Exp. 12: Odor

Gently noted the ``different'' and sharp odor of the gas.

Exp. 13: Test with indicators

Turmeric paper, blue liquor (litmus), cabbage juice were used and the changes in color were noted (different than the color produced with nitric acid).

Exp. 14: Solubility noted

A jar of ammonia was inverted over a container of water, the rise in the water level demonstrating the solubility of the gas in water.

Exp. 15: Mass of the gas

Determine the weight of one gallon of the gas. This was probably displayed on a chart rather than demonstrated. The storied pig's bladder method has now given way to accurate measurements using glass globes.

Exp. 16: Effect on oily mixtures

Ammonia was added to a mixture of oil and water. It is not clear what Faraday had in mind.

Exp. 17: Acid and alkali reaction

Using an indicator such as litmus, the neutralizing effect of ammonia and an acid was demonstrated.

Exp. 18: Test salts with indicators

Different neutral salts were tested with a blue liquor (litmus) indicator and the color of the indicator was noted.

Exp. 19: Test other salts with indicators

Non-neutral salts such as ammonium chloride were tested with the same indicator and the color noted.

Exp. 20: Heat reddened turmeric

Turmeric is red in an alkaline solution. It is assumed that Faraday added turmeric to a solution of ammonia and the color changed to a yellow-brown.

Exp. 21: Burn a feather

Demonstrated the formation of ammonia by HCl(g) test.

Exp. 22: Burn ammonia with oxygen

Ammonia was burned in an atmosphere of oxygen forming oxides of nitrogen and water vapor.

Exp. 23: Decomposition of gaseous ammonia

When heated strongly ammonia decomposes to N₂ & H₂. Recall the textbook discussion of the Haber ammonia synthesis. (note odor)

Muriatic Acid (hydrochloric acid)

Exp. 24: Preparation of the acid

Demonstrated the preparation of hydrochloric acid by heating oil of vitriol (sulfuric acid) and sodium chloride.

Exp. 25: Test fumes produced (from above reaction) with litmus

Tested the gas produced with moistened indicator paper to demonstrate that an acid was formed.

Exp. 26: Add water to the gas produced

Water was added to a container of the gas collected in Exp. 24, to demonstrate the solubility of the gas. Alternatively, a container of the gas may have been collected by air displacement and then inverted over a container of water.

Exp. 27: Collect the gas over mercury

The common method of collecting water soluble gases was by the downward displacement of mercury from containers inverted in a pneumatic trough.

Exp. 28: Demonstrate degree of solubility of the gas

Demonstrated the difference in the volume of a bottle of the gas and the volume of gas remaining undissolved when it is inverted over water thus illustrating the high degree of solubility.

Exp. 29: Display mass of the gas

The mass of a standard volume of this gas was probably determined in the same manner as in Exp. 15 and displayed on a pre-prepared chart.

Exp. 30: Place a lighted candle in the gas

Demonstrated the non-combustibility of the gas (the candle was extinguished).

Exp. 31: Test with indicators

Tested the gas with moistened litmus paper or tested a solution with litmus or cabbage liquor, noting the acidic character.

Exp. 32: Demonstrate solubility in water

Probably the same as Exp. 26. He apparently used both methods to illustrate the solubility of hydrogen chloride.

Exp. 33: Neutralize alkali solutions

Used an alkaline solution with turmeric or cabbage liquor. Added the acid and noted the color change. (Cabbage liquor is green in a base and red in acid).

Exp. 34: React ammonia with muriatic acid

Demonstrated the reaction of these two colorless gases which, when brought close together, form a white (smoke-like) solid.

Exp. 35: Heat sal ammoniac

Heated sal ammoniac (ammonium chloride), causing decomposition into ammonia and muriatic acid gas.

Chlorine

Exp. 36: Preparation of chlorine

Heated black oxide of manganese with muriatic acid and collected the gas (probably by water displacement).

Exp. 37: Prepration of chlorine

Another method of preparation was demonstrated by heating red lead and muriatic acid.

Exp. 38: Note physical properties

After collecting a bottle of chlorine, the greenish-yellow color of the gas was noted as was the odor and its deleterious effect on the lungs.

Exp. 39: Test gas for combustion

The gas was tested with a candle (candle extinguished). Tested gas with metals and determined which metals burn in the chlorine.

Exp. 40: Burn copper and antimony

Copper leaf and antimony were ``burned'' in a bottle of chlorine.

Exp. 41: Demonstrate bleaching properties

Indigo, cabbage liquor, colored cotton and colored paper were added to chlorine to demonstrate the bleaching property of the gas.

Exp. 42: Use as an air purifier

Demonstrated the odor and bleaching properties of chlorine and suggested that these properties would render it suitable as an agent to purify air.

Exp. 43: Determine weight of a fixed volume of the gas

Displayed the weight of a volume of this gas determined in the same maner as in Exp.15.

Exp. 44: Combustion with hydrogen

Burned hydrogen in a jar of chlorine, noting that the product was muriatic acid. Observed the colors and solubility of the product in water and its effect on litmus solution.

Editors

Michael P. Kelly, R. James Kurtz, Nancy LeMaster, Sara McCoy, Judith Moody, Daniel Morton, Gerald Munley, and John Oliver.

Woodrow Wilson Leadership Program in Chemistry lpt@www.woodrow.org
The Woodrow Wilson National Fellowship Foundation webmaster@woodrow.org
CN 5281, Princeton NJ 08543-5281 Tel:(609)452-7007 Fax:(609)452-0066