How many grams of caustic soda are needed to saponify the fat I have weighed out?

Q: How many grams of caustic soda are needed to saponify the fat I have weighed out?

If you are blending different fats and oils you can answer this question for each one separately and then add the weights to get the total weight of caustic soda. Multiply the total weight of caustic soda by a factor of 0.95; it is far better to have a finished soap with excess fat than one with excess caustic soda. Weigh out your caustic soda on a balance and record the weight in your notebook. Weigh out twice that amount of water in a glass measuring cup or beaker and record the weight in your notebook. Stirring with a glass rod or plastic spoon, slowly add your caustic soda to your water—if you add water to caustic soda, the caustic soda will cake up and dissolve more slowly. The water will get hot as the caustic soda dissolves. Continue stirring until the caustic soda is completely dissolved. By this time, you should have hot melted fat on the stove and hot caustic soda solution in a beaker.

They say that a watched pot never boils, but it never cools either. You are about to mix the oil and caustic soda solution together, but as with salad dressing, oil and water don't mix. This is especially true of hot oil and water, so you will get the best results if you allow both ingredients to cool down to between 38 and 43?C, 100 and 110?F. A thermometer will keep you honest, but as long as you can hold them in your bare hands comfortably, you are probably alright. In my experience, the most frequent reason for failed soap is that the soaper got impatient and mixed the oil with the caustic soda too soon.

When the fat and caustic soda have cooled sufficiently, use a funnel to pour the fat into your 2-liter pop bottle. Add the caustic soda solution, put the cap on the bottle and give it a few shakes. You now have what amounts to caustic salad dressing—the oil and water mix initially, but may separate over time. As long as the mixture is smooth and creamy, you are fine, but if it begins to separate, give the bottle another shake. When the mixture no longer separates, you can let it rest. A tallow or shortening soap may solidify in an hour or so; a lard or olive oil soap may take up to two days.

The saponification will proceed more quickly if the mixture is kept warm than if it is allowed to cool. Because the saponification reaction is exothermic, simply insulating a large batch of soap is sufficient to keep it warm, but a small batch may need some help. I like to place my sealed 2-liter bottle in a pot of hot tap water to keep it warm. Don't watch this pot or fret about it, but whenever it occurs to you in the first couple of days, replace the water with hot tap water. If you forget to change the water, it's no big deal—the soap may just take a little longer to cure.

The curing time will vary from one fat to another, but after a week your soap should be ready for testing. With a knife, slit the pop bottle open and peel it apart to release your soap. If you have done your work correctly, you will have a single solid cake of soap with very little extraneous water. Cut a sliver the size of a raisin from this cake and place it into an empty bottle with a cup or so of hot water. Put the cap on the bottle and shake it. If you have succeeded in making soap, the bottle will fill with soap suds after a bit of shaking. If it doesn't, then either you had too little caustic soda in your mixture or the soap is not sufficiently cured. As a second test, wipe a piece of wet pH test paper against your soap. If it turns blue, then either you had too much caustic soda in your mixture or the soap is not sufficiently cured. If your soap fails either of these tests, allow it to cure for a few more days and then test it again. When your soap is finished, you can slice it into bars of a convenient size.

With a bottle of soap suds, you can explore one more aspect of soap manufacture. Make a good, strong soap solution and add some salt to it. The fatty acid salts are less soluble in salt water than they are in fresh water and so they will precipitate from the solution. The soap, that is, the fatty acid salts will float to the top while the glycerol stays in solution. Separating the above from the below allows us to produce glycerol as a by-product of soap manufacture. Glycerol will be an important player in the development of explosives and plastics, as we shall see in Chapter 27.

Quality Assurance

Record the weights of the fat, caustic soda, and water that went into your pop bottle and compare these to the weight of the soap you produced. The soap is satisfactory if it makes suds and has a pH no higher than 8. Tape your yellow or green pH test paper into your notebook as a keepsake.

Chapter 20. Leblanc (Soda)

A Most Easie Way of Acquiring Spirit of Salt Together With the Salt Mirabile. R. of common salt two parts, dissolve it in a sufficient quantity of common water; pour A upon the solution; put the mixture into a glass Body, or a glass Retort well coated, or else into an earthen Body or Retort. If a Body, set on an Head, and begin to destil with Fire of sand, encreasing your Fire gradually; with the first heat comes off the unsavory Phlegm, which gather apart; when the Liquor comes forth sowrish, change your Receiver and receive the sowre spirit: Continue the operation till no more spirits will arise, then let out the Fire, and permit the Vessel to stand in sand till all is cooled, when cold, take it out, and if it be unbroke, fill it again with the aforesaid matter, and proceed as we taught: The Phlegm is not to be cast away, but must be kept, that in it may be dissolved Salt (because it is better than common water) for another

destillation. Thus from every pound of salt you will have lb. 1 of the best and most pure spirit. Dissolve the salt remaining in the Body or Retort (if neither be broke) in Water, filter and evaporate the Water, let it crystallize, the Crystals will be white, endowed with wonderful Virtues, to be declared here following.

— Rudolf Glauber, Miraculum Mundi, ca. 1658 AD [1]

20.1.

When I was born in 1742 the king was on his throne, God was in his heaven, and all was right with the world. It would not last. I was orphaned at the age of nine and apprenticed to an apothecary, where I learned my chemistry from sacred texts such as the one quoted above. I studied surgery at college, graduating as Nicolas Leblanc, MD. In 1780 I became physician to the Duke of Orleans and with his patronage devoted myself to the winning of a prize of 2,400 livres offered by the Acad 魩 e des Sciences for "anyone who should find the most simple and economical method to decompose in bulk salts from the sea, extract the alkali which forms their base in its pure state, free from any acid or neutral combination, in such a manner that the value of this mineral alkali shall not exceed the price of the product extracted from the best foreign sodas."[2] You are probably wondering why the Acad 魩 e would offer such a prize. I will tell you.

See, the glass business had been using potash or soda ash as a flux ever since about the twenty-fifth century BC (Chapter 13); the paper business needed alkali ever since the first century AD (Chapter 14); and the soap business had filled out by the eighteenth century, which increased the demand for alkalis even more (Chapter 19). And ever since God was a child, folks had been making potash and soda ash by leaching ashes (Chapter 8), lime by burning limestone (Chapter 10), and caustic soda by reacting soda ash and lime (Chapter 15). So alkali was a pretty good business by the eighteenth century, what

Any country that had a glass, paper, or soap industry needed soda and to get it they tried burning all kinds of stuff to get ash. The saltwort plant, which grew mostly in Spain and the Canary Islands, was about the best thing to burn, on account of its ash, called barilla, contained about 20% soda. If you didn't want to have to kiss up to Spain, you could burn seaweed, which they did in Ireland and Scotland, but its ash, called kelp, contained only about a third as much soda as barilla did. No matter what you burned, you had to burn lots of it to get a little ash, and not all of that ash was soda. As the eighteenth century wore on, the supply of ash couldn't keep up with the demand for soda and the price doubled from 1750 to 1790. Now the French Academy of Sciences was worried about the dependence of domestic glass and soap on imported soda, so they offered a prize to promote the foundation of a domestic soda industry which would liberate France from Spanish barilla and Scottish kelp.

Pardon me; this was my story. Sorry.

Earlier, in 1736 the French agriculturalist Henri Louis Duhamel du Monceau had revealed that soda and sea salt were salts of the same base, now known as sodium hydroxide. This being so, he proclaimed that it was possible, in principle, to make soda (sodium carbonate) from sea salt (sodium chloride). This information came down to me —

Like a spider.

More like a revelation, really, and I began to look for an intermediate between salt and soda. Glauber's salt (sodium sulfate) was well known among doctors (Chapter 18) and was easily produced from sea salt and sulfuric acid. If it were possible to convert Glauber's salt to soda, it would prove even more mirabile than had previously been imagined. Several people had taken this approach to the problem and after a thorough review of the successes and failures of my contemporaries—

For inspiration.

—I devised a process for this conversion involving the calcination of limestone, coal, and Glauber's salt in a furnace to produce "black ash," from which soda could be extracted by recrystallization. The Acad 魩 e had increased the prize to 12,000 livres in 1789 and two years later I was granted a patent from the king. I set up a factory at Saint- Denis with the financial backing of the Duke; at its peak the factory was producing 320 tons of soda per year. Unfortunately, the 1790's were not the best of times for the French nobility, as the Comit 頤 u Salu Public provided a brisk trade for the guillotine business. The Duke lost his head in 1793, the plant was confiscated, and the Acad 魩 e des Sciences abolished.

Now, all I wanted to do was to found a domestic soda industry for the benefit of French glass, paper, and soap makers, collect my prize, and settle down to a life of quiet contemplation. But in the space of a few years the king was de-throned, God seemed to have taken a holiday, and all was not particularly right with my world. Seeing the writing on the wall, I surrendered my patent to the Comit 鼯 I > and the details of my process were published in 1797 in the Annales de Chimie. In 1802 Napoleon finally came to the realization that cheap domestic soda would be good for France and returned the now- derelict factory to me, but balked at the suggestion that he make good on the Acad 魩 e's promised prize. I tried to make a go of it, I really did. But by the time I was allowed to resume my vocation, the secrets of my process had wandered far and wide.

Like spiders.

Like prodigal spiders, perhaps. Facing stiff competition from ungrateful imitators with more capital, my business failed. I must confess that I sank into depression and in a fit of melancholy shot myself in 1806.

By 1810, French soda plants were making 15,000 tons of soda per year. Meanwhile, back in England there was a stiff salt tax which discouraged the black ash process from hopping the Channel, but the salt tax was repealed in 1823.

May I continue?

I thought you were supposed to be dead. So, with the salt tax gone and with inspiration from Leblanc, James Muspratt opened a black ash soda works at Liverpool, near the Cheshire salt fields. Pretty soon everybody and his dog had a soda plant. By 1852, the French soda production of 45,000 tons would be topped by the English production of 140,000 tons per year.

Largely subsuming the chamber acid industry, Leblanc soda would become the foundation of a diversified chemical industry with products that included sulfuric and hydrochloric acids, soda, lime, salt cake (Glauber's salt), and caustic soda. Growing from scattered factories to immense complexes, soda manufacturers would, by the end of the nineteenth century, introduce such modern innovations as toxic waste dumps, water pollution, and acid rain. This pollution would create a climate of government regulation which would force manufacturers to find markets for former waste products. Eventually these new chemicals would become even more profitable than the original ones, leading to another round of industrial growth and rendering the word chemical synonymous with the word poison in the popular culture. But I am getting ahead of myself.

Notes

[1] Reference [18], pp. 31-32. [2] Reference [52].

20.2.

By the eighteenth century, increasing quantities of soluble alkali were in demand by three major industries. The glass industry relied on sodium or potassium carbonate as a flux for lowering the melting point of silica. The paper industry preferred soluble sodium hydroxide to marginally soluble calcium hydroxide for hydrolyzing lignin from pulp. The soap industry preferred sodium hydroxide to potassium hydroxide for saponifying oils and fats; the sodium salts of fatty acids are less hygroscopic than the potassium salts, which makes it easy to produce solid cakes of soap from sodium hydroxide. Since sodium hydroxide is easily produced from sodium carbonate and calcium hydroxide, the demands of all three industries would be satisfied if only there were a plentiful, inexpensive supply of sodium carbonate.

From remote antiquity, sodium carbonate had been available from two major sources. It occurred as a mineral in the deserts of the Middle East, having been deposited when water evaporated from ancient, alkaline seas. The Latin name for this mineral was natron, whose first two letters gave us the symbol for the element sodium. The Egyptian name survives in the name for the mineral trona, sodium sesquicarbonate, a 50/50 mixture of sodium carbonate and sodium bicarbonate. Where this mineral is available, other sources of soda cannot compete; there is nothing more economical than digging the material you need right out of the ground.

Trona is not a common mineral, however, and in most parts of the world soda has traditionally been produced by burning plant materials, the ashes of which contain sodium and potassium carbonates. Inland plants are richer in potassium and the soluble alkali extracted from their ashes is called potash, from which the element derives its name. Marine plants are richer in sodium and among the richest sources of soda are saltwort and seaweed. Whatever the source of alkali, a great deal of plant material must be burned to produce a little ash and not all of that ash is soda. Table 8-1 shows that 1000 pounds of beech wood yields only 1 pound of potash. Similarly, 1000 pounds of dry kelp yield at most 2 pounds of soda.[1] When the demand for soda exceeds the supply from mineral and vegetable sources, an enterprising chemist would look for another source of soda and one obvious candidate is ordinary salt.

Salt was indispensable for the preservation of meat in the time before refrigeration, and it continues to be produced by time-honored methods. Salt-makers in hot climates produce salt by flooding shallow ponds with sea-water and allowing the Sun to drive off the water. In cold climates they freeze salt water; pure water-ice freezes out first, leaving concentrated brine to be evaporated to dryness. Salt-makers who are unfortunate enough to live in moderate climates must burn fuel to drive bejeezical water from brine. Salt can be extracted not only from modern seas, but from ancient ones as well; the dried remains of ancient oceans are mined or quarried for the mineral, halite. With sodium from sodium chloride, we need only find a way to combine it with carbonate to make soda.

Figure 20-1. Halite

The Leblanc process consists of three furnaces and a lixiviator, as shown schematically in Figure 20-2. In the first furnace, the salt cake furnace, sodium chloride and sulfuric acid engage in a typical metathesis reaction, as shown in Figure 20-2(a). The products are solid sodium sulfate and gaseous hydrogen chloride. During the first half-century of the Leblanc era, there was little commercial demand for hydrogen chloride and it was simply sent up the chimney. If the neighbors complained, which they often did, the soda-maker simply built a taller chimney; chimneys of 400 feet were not uncommon. Alternatively, hydrogen chloride gas was absorbed into water, producing hydrochloric acid. With little demand for this acid it was frequently run into the nearest river. This seems irresponsible by modern standards, but the point of this first step is, after all, to get rid of the chloride and keep the sodium.

Figure 20-2. The Leblanc Soda Process

The second furnace of the Leblanc process, the black ash furnace, reacts sodium sulfate with coal and limestone at red heat, as shown in Figure 20-2(b). Bejeezical carbon dioxide flies the coop leaving black ash, a mixture of sodium carbonate, calcium sulfide, and residual coal and limestone. The main product, sodium carbonate, is soluble in water while the waste products are not. The third step of the process lixiviates the black ash with water, leaching out the soda and leaving a solid combination of blackened calcium sulfide and limestone known in the trade as tank waste. The final furnace evaporates the wash water, which deposits its cargo of soda. If this wash water is boiled down and left to cool, the result is washing soda, Na2CO3?10 H2O. If it is calcined at red heat, the result is

soda ash, Na2CO3. The schematic may look complicated, but the first two furnaces

hearken all the way back to Figure 1-3 and the right half of the figure is identical to Figure 8-1. Just remember that reactants enter from the left of the figure, waste product