A requiem for amateur chemistry

Bidding farewell to classic experiments.

I grew up in a household full of books; one day, I stumbled across a couple of vintage amateur chemistry titles from the 1970s and 1980s. I quickly fell in love with the dazzling and sometimes dangerous experiments that offered insights into the invisible machinery of life.

Alas, my childhood also marked the final years of amateur chemistry as a socially acceptable pursuit. The global War on Drugs had already started to nip at the edges; the War on Terror delivered another blow. The assault came from other directions too: for example, in the United States, the Consumer Product Safety Commission found it worthwhile to raid the sellers of chemicals that could be used to make bootleg fireworks. Tech purges followed: over the past decade, a number of chemists lost their YouTube channels, eBay cracked down on the sale of common reagents, and PayPal went after independent shops.

Today, you can still purchase a chemistry set for your children, but the kit will contain little more than baking soda, citric acid, and some pH strips. With a bit of know-how and patience, a resourceful parent can build a competent homeschooling lab, but the task is getting more difficult with every passing year.

It is equally difficult to source ideas for the curriculum. Many classic amateur chemistry books are out of print, and there is little incentive to publish more. In a vain attempt to buck the trend, I figured I’d catalog some of the more colorful experiments I remember from my childhood — at least the ones that didn’t require specialized equipment or unusually toxic chemicals:

• DIY photographic paper. There are two common routes. The cyanotype process produces striking blue images and uses a mix of ferric ammonium citrate and potassium ferricyanide, with hydrogen peroxide as a developer and tap water as a wash. The alternative approach involves brushing on silver nitrate and table salt to precipitate light-sensitive silver chloride; citric acid is sometimes included as a sensitizer, too, followed by potassium thiocyanate as a wash. The paper works with pinhole cameras, or can be used to reproduce the outlines of leaves, toys, and other items placed on top of the sheet.

• Invisible ink. There are countless versions of this experiment, but perhaps the most striking variant involves writing with a 1% solution of phenolphthalein and then moving the paper over a plate moistened with several drops of ammonium hydroxide. This momentarily reveals the letters only to have them fade away as the ammonia dissipates. Another cool variant involves writing in cursive with a solution of potassium nitrate, touching the dried text with a red hot nail, and then watching the letters burn away.

• Homemade Rayon. Rayon is an early semisynthetic fiber made from solubilized cellulose. The original production method involved mixing copper nitrate with sodium hydroxide, and then dissolving the resulting precipitate in ammonium hydroxide. This is known as the Schweizer's reagent. A saturated solution of cellulose in this complex is then prepared and extruded into a neutralizing batch of dilute acid. A syringe with a needle will do.

• Thunder in a test tube. A small amount of concentrated sulfuric acid is poured into a test tube; a layer of ethanol is then carefully poured on top. A single grain of potassium permanganate is dropped into the tube; as soon as it touches the layer of sulfuric acid, it is dehydrated to form unstable manganese heptoxide that violently reacts with alcohol — producing a flash of light and an audible crack. A more dangerous version of this experiment involves preparing a (very small) pile of permanganate, wetting it thoroughly with several drops of sulfuric acid, and then adding a drop of alcohol from a safe distance. Poof!

• Silver mirror. This classic experiment employs silver nitrate and ammonium hydroxide (Tollens' reagent). The addition of glucose produces a beautiful metallic mirror on the inside of a laboratory beaker. A neat party trick with uses in analytical chemistry. Leftover reagent should be neutralized and discarded to avoid trouble.

• Tin trees. The electrolysis of tin(II) chloride in a Petri dish produces bifurcated dendritic growths that resemble tree branches. It is an interesting counterpart to the better-known electroless copper plating experiment.

• Shake-detecting liquid. Methylene blue mixed with glucose and sodium hydroxide is quickly reduced to a colorless solution. Swirling or shaking the flask introduces atmospheric oxygen and briefly oxidizes the dye, making it brilliant blue for a while.

• Chemical garden. Individual crystals of metal salts form colorful tree-like growths in a solution of sodium silicate. This is due to the repeated formation and destruction of a semipermeable membrane. Copper, zinc, iron(II), iron(III), calcium, and aluminum salts are common picks.

• Juice “caviar”. Kitchen-safe chemistry. A flavored drink mixed with food-grade sodium alginate is added dropwise to a solution of calcium chloride or lactate, forming edible caviar-like capsules.

• Polyvinyl alcohol slime. Polyvinyl alcohol is slowly dissolved in boiling water, and then mixed with a small amount of dissolved borax. The result is a Ghostbusters-style slime, optionally dyed with food coloring. Different ratios can be used to yield a runny goo or a bouncy polymer. Lots of fun for kids - and a nice example of cross-polymerization.

• Crystals of metallic copper. A low current of about 10 mA is supplied to a bath of copper acetate via a sacrificial copper anode (short video by author). The experiment takes several weeks. In the meantime, it can be fun to grow richly-colored and large crystals of copper sulfate or potassium ferricyanide; these are much nicer than crystals of table salt.

• Hot ice. Sodium acetate trihydrate dissolves in its own water of hydration at around 60° C; if undisturbed and free of particulates, this solution can be easily supercooled to room temperature. When poked, it undergoes flash crystallization and heats up quite a bit (short video by author).

• Color-changing roses. A solution of table salt can be electrolyzed to capture a small amount of chlorine gas in a submerged upside-down beaker. A red rose placed in that atmosphere will turn yellowish-white. Chlorine is toxic, but as long as the amount produced is small, it’s a fairly safe experiment.

• Prussian blue. A deep blue pigment forms as a precipitate after mixing potassium ferricyanide with iron(III) chloride. The dried precipitate can be made into paint by adding a binder such as egg yolk and water.

• Chevreul’s salt. An unusual and colorful mixed-valence copper salt can be precipitated by heating a fresh mixture of copper sulfate and potassium metabisulfite (author’s video). Needs to be done outdoors.

• Starch test. Iodine has a characteristic reaction with starch that can be used to detect the composition of processed foods. Nowadays, iodine is unavailable due to its use in the production of methamphetamine; but it can be prepared from iodide salts. The element is interesting in other ways, too: it sublimates to form purple plumes of gas and re-crystallizes on nearby cool surfaces.

• Copper nitrate. Although a rather simple reaction, dissolving copper in nitric acid is visually striking: it yields a deep green solution and produces a heavy plume of orange-colored nitrogen dioxide. Not to be attempted indoors.

• Extreme dehydration. Paper, cloth, table sugar, and other carbohydrates are easily charred by concentrated sulfuric acid. A good demonstration to convey the importance of lab safety protocols.

• Nitrated cellulose. With utmost precautions and only in small quantities, a mixture of nitric and sulfuric acid can be used to nitrate cellulose. Nitrated paper or cotton balls will look the same as before, but will burn instantly and completely when ignited. Nitrocellulose is also soluble in acetone and other organic solvents; in that form, it is commonly used as a high-gloss wood finish.

• Glycerin fire. Potassium permanganate is a strong oxidizer; a small pile soaked with several drops of glycerin will spontaneously ignite within a minute or so. Must be done outdoors.

• Chemiluminescence. A particularly striking variant involves adding an alkaline solution of luminol dropwise to a mixture of potassium ferricyanide and hydrogen peroxide (author’s video). That said, luminol is a relatively exotic reagent, and many other variations exist.

Most of these experiments carry risk. Strong mineral acids and bases can cause severe burns; gases such as chlorine or nitrogen dioxide can cause lung injury; and even fairly benign reagents can be harmful if ingested or splashed into the eyes. But let me put it this way: growing up poor in a single-parent household, amateur chemistry kept me from doing far worse things.

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