Frigorific Solutions of the Regency

Despite what you may be thinking, this particular f-word is perfectly respectable. In fact, it is quite learned, as it is now, and was during the Regency, the scientific term for things that produce cold. In fact, the first documented use of the word in print, according to the Oxford English Dictionary, was in 1668, when it was used by Robert Boyle in an article he wrote for the Royal Society about the "frigorifick" power of the combination of ice and salt. Last week, I explained how saltpetre could be used to reduce the temperature of water in order to chill wine. That mixture of saltpetre and water comprised one type of frigorific solution. There were other salts available during the Regency which could also be used to chemically produce or increase cold when used in combination, usually mixed with water and ice. In the right combinations, some of those solutions could even produce temperatures well below the freezing point of water.

The freezing facts about frigorific solutions …

Even in ancient times, peoples in a number of different cultures harvested ice and hard-pack snow for use in cooling food and beverages. Some of the more observant members of those cultures noticed that when ice was combined with certain "salts" in solution with water, that solution could produce temperatures even lower than the ice itself. Of course, they did not know specifically how much colder until the latter half of the seventeenth century, since it was only then that a reliable thermometer had been developed by which it was possible to measure temperature precisely. Studies of the frigorific properties of various salts in solution continued though the seventeenth century, well into the nineteenth and a number of articles were published on the results. By the Regency, the various cooling properties of the salts noted below were fairly widely known.

Sodium chloride, what is known as common or table salt, was usually the least expensive salt which was used to make a frigorific solution. Unlike saltpetre, sodium chloride could not cool just water, since it did not create an endothermic reaction as it dissolved in the water. However, it could drop the freezing point of an ice and water mixture, depending upon the amount of salt added. Plain water freezes at 32º Fahrenheit, but salt dissolved in the water makes it denser so that it will not solidify until it reaches a much lower temperature. As long as the frigorific solution remains fluid, it can transfer the cold to whatever is immersed in it. The more salt in the water, the lower the temperature needed to freeze the water, thus the more cold that can be transferred to that which is immersed in it. Like saltpetre, salt could also be recovered from the cooling solution once it had served its purpose. However, it was so inexpensive that it was seldom worth the effort, or the fuel, to recover it by boiling down the solution.

Sugar would serve the same purpose as salt in a frigorific solution, by increasing the density of the solution, but sugar was much more expensive. However, in the making of ice cream, sugar was the ideal ingredient by which to reduce the freezing point of the ice cream mixture itself. Though it may seem counter-intuitive, in order to achieve a smooth and creamy texture, without the formation of ice crystals, the ice cream mixture should freeze slowly while being stirred regularly. The addition of sugar would increase the density of the ice cream mixture, thus reducing the freezing point and avoiding the formation of ice crystals as the mixture solidified.

Sal ammoniac was another salt which could be used to create a frigorific solution. The modern name for this chemical is ammonium chloride, but like saltpetre, it got its common name from the ancient Romans. They found large deposits of it near a Temple of Amun, and so they called it "salt of Amun." During the Regency, it was also known as muriate of ammonia. Sal ammoniac was once used as a treatment for sore throats. Finely powdered, it was placed in a paper cone, the small end was placed deep in the patient’s throat and the person holding the cone gently blew the powder through the small end. The dust would settle on the irritated tissues and the patient would get instant relief from their pain. In the past, sal ammoniac was often used in the making of various candies and other confections, but it is seldom used for that purpose today.

During the Regency, sal ammoniac was imported from the north coast of Africa, principally from Egypt. It was made from the soot given off by camel dung fires. Sal ammoniac could not be used alone in a cooling solution, since like common salt, it would not result in an endothermic reaction as it dissolved. In most cases, sal ammoniac was used in conjunction with saltpetre since it had the effect of reducing the temperature lower than with saltpetre alone, and extending the period during which the frigorific solution retained the lower temperature. In most formulas, sal ammoniac and saltpetre were used in equal parts to create a frigorific solution. When used together in a water and crushed ice solution, the temperatures could be brought down to 15º F. or less. Sal ammoniac was more than twice as expensive as saltpetre, costing a shilling a pound or more during the Regency. However, like saltpetre, it could be recovered by boiling down the used cooling solution, or allowing the liquid to evaporate away. The resulting crystals could be re-powdered and reused indefinitely.

Because sal ammoniac was so expensive, a common substitute was Glauber’s salt. Known today as sodium sulfate, the Dutch chemist who discovered this salt in the seventeenth century, Johann Rudolf Glauber, called it sal mirabilis, the miraculous salt, because it had a number of medical applications. It was frequently used as a general laxative through most of the nineteenth century. The main source of Glauber’s salt during the Regency was the mineral mirabilite. There were deposits of this mineral across Europe.

Glauber’s salt could be mixed with equal parts of saltpetre in a plain water solution, to achieve a temperature in the mid-forty degrees. But when mixed with equal parts of saltpetre and sal ammoniac, in a solution of chipped ice and water, the temperature of that frigorific solution could be brought down to the high twenty degree range, well below the normal freezing point of plain water. The addition of Glauber’s salt would also extend the period during which the solution was able to retain this much colder temperature. The main advantage of using Glauber’s salt was that is was fairly cheap, since it could be had for between two and three pence per pound, and the supply was plentiful. The main disadvantage was that Glauber’s salt could not be recovered by boiling down the frigorific solution to which it had been added or allowing the water in that solution to evaporate.

In most private households during the Regency, the use of a chemical refrigerant, such as saltpetre, alone, or blended with other salts, was typically only done in cases where there was no ice to be had, or not enough ice to serve the purpose. For example, if a large social gathering, such as a ball, was planned, but there was not enough ice available to cool all of the bottles of wine which were expected to be served that evening, then the cooling power of the ice could be enhanced and expanded with the use of some combination of these salts in a solution of water and finely chipped ice. Dinner wines were expected to be served only slightly chilled, so the wines for that evening’s dinner might be cooled in a frigorific solution of some ice, and a large percentage of saltpetre and sal ammoniac, perhaps with the addition of common salt or Glauber’s salt. Sweet dessert wines and sparkling wines, like champagne, were expected to be served very cold. Therefore, the dessert wines for that evening and the champagne which was to be served at the ball and the supper, would all be immersed in a frigorific solution of water, a lot of finely crushed ice and saltpetre, sal ammoniac and Glauber’s salt or common salt. In such cases, it appears that Glauber’s salt would be a better choice, since it could bring the temperature of the solution down a bit more than common salt, and keep it colder for a longer period. Though it was a bit more expensive than common salt, Glauber’s salt seems to have been the preferred salt, in combination with saltpetre, sal ammoniac and iced water for keeping wines cold for the duration of a ball which could last several hours. For a shorter event, common salt would be sufficient.

Frigorific solutions were almost certainly used on a more regular basis at commercial premises, such as those involved in the daily production of ices, ice creams and other frozen treats. The use of just crushed ice or crushed ice in water would not lower the temperature sufficiently to freeze fruit ices or ice creams. The addition of various combinations of these salts to a slushy ice/water mixture would drop the temperature of the solution below the freezing point of water, while keeping it liquid. A frigorific solution was best able to transfer cold when it was in a fluid or semi-fluid state. Therefore, when Gunther’s, or any other confectioner, made ices or ice cream during the Regency, they would have used a frigorific solution which remained fluid well below the freezing point of water in order to ensure the best transfer of cold to their frozen confections.

One summer in Oxford, a local confectioner was unable to procure the natural ice he needed to make ices and ice creams. Since this was typically the season during which the sales of such frozen confections was crucial to his business, he applied to a don at the college who was known to have conducted a number of experiments in the artificial production of cold. Dr. Richard Walker had published several papers and pamphlets on the various salts which could be used for the making of frigorific solutions, but this was an opportunity to employ his theoretical knowledge in a practical application. After some consideration, Dr. Walker determined that the most efficient method was to create ice, which the confectioner could then use with his existing equipment in the making of ices and ice creams. A large apparatus was constructed in which several channels made of tin could be surrounded by his frigorific solution. This apparatus was set up in a cool cellar. Each night, the tin channels were filled with plain water and were surrounded by a solution of water into which had been dissolved a large amount of equal parts saltpetre and sal ammoniac. This was left overnight, and each morning, several pounds of ice was taken from the tin channels. The confectioner could then use this artificially-made ice just as he would have used natural ice to make his frozen confections. Each day, he boiled down the salt and water solution to recover the salts, which he then powdered and reused each night. In this way, the confectioner made enough ice each night to be able to make ices and ice creams for his customers every day throughout the summer.

The use of natural ice for cooling was always preferred during the Regency, in part because it was cheaper, but also because it required much less effort and no technical knowledge of chemistry, as did the use of frigorific solutions. There would have been a few, with a great love of scientific novelty, who may have used such frigorific solutions to cool their wines at parties to amuse and entertain like-minded friends. For the most part ice was used in private homes to chill wines and other dishes. When ice cream was made, it was most often accomplished with the addition of common salt to a crushed ice and water mixture. That frigorific solution is so effective, we still use it today in the making of homemade ice creams. The main use of frigorific solutions was by commercial establishments, such as confectioners, who needed the extreme cold to produce a high volume of frozen specialty confections. It must also be noted that only those with a great familiarity with the language of science would have used the term "frigorific." The term does not appear to have been used in anything but scientific publications throughout the decade of the Regency and well into the reign of Queen Victoria.

Even in the Regency, there were still some people, even a few doctors, who believed that the use of these salts for cooling was a dangerous risk to one’s health. But on the other side of the Age of Enlightenment, those who feared the use of frigorific solutions were very definitely in the minority. There were also still a scattering of people who believed that the consumption of chilled beverages and frozen confections was injurious to the health. But such people were usually thought ignorant and superstitious and there do not seem to have been very many of them among the Beau Monde in the days of the Regency.

Though the use of frigorific solutions was not widespread during the Regency, there is no reason why a clever author cannot make use of one or more of them to enhance a story where deep cooling is needed. Perhaps a character is a devotee of science and uses such solutions to cool beverages for his guests, especially those also interested in things scientific. To add a bit of conflict, perhaps his wife, or some other member of his household, is suspicious or frightened of chemically-enhanced cold, and/or believes that drinking chilled beverages is unhealthy. A host, maybe along with his butler, find themselves in a difficult situation when they cannot get enough ice to cool all the bottles of wine which they are planning to serve at some grand event. Either the host, or his butler, know how they can enhance and extend the ice they do have by the addition of some combination of salts to create a frigorific solution. Thus, they will be able to ensure all their wines will be properly cooled, despite a shortage of ice, with none of their guests the wiser. Dear Regency Authors, how might you make use of a frigorific solution in one of your upcoming stories?