Early days

The earliest surviving references to the construction of the original building on Bath Road from 1807 (and there are very few) are all solely concerned with baths. Yet it is clear that salts must have been produced here from day one, even if they were not immediately available to the public. In October of that year Henry Thompson was granted a patent for a method of impregnating Cheltenham or other mineral waters with different gases and combining other substances with the waters to create salts.

The work to enable the patent to be obtained must have been undertaken in the engine house that adjoined the baths, as shown on the floor plan included in Dr Jameson’s Treatise on Cheltenham Waters of 1809. The cast iron steam boiler held 287 gallons of water, heating the entire building and baths while at the same time evaporating water for making salts.

Having obtained his patent, Thompson must have ramped up production for public sale as by August 1809 advertisements for Thompson’s Genuine Crystals of Cheltenham Salts are being published as far away as Dublin. Business is clearly brisk as at some point between now and 1814 the building is considerably enlarged, not for bathing but for the production of salts.

---

Supplying the water

In 1809 Henry Thompson repurposed his original spa, Hygeia House, into his own private residence and opened a new wooden structure – the Montpellier Spa – where people could take the waters. Both these properties had wells on site, as had the laboratory, but the latter needed a particularly substantial water supply to keep up with the increasing demand of a successful business, so from 1811 Thompson took steps to ensure an inexhaustible supply by sinking dozens of wells all over his land in Lansdown and Montpellier.

The General Guide to Cheltenham by JK Griffith (1818) included a description provided by Thompson himself of the sinking of the well situated nearest to the premises: ‘After passing through the soil, they came to a bed of sand, which continued for 12 feet, at which depth fresh water was found; under this was a bed of blue clay, in which, at the depth of 15 feet, or 27 feet from the surface of the sand, a saline chalybeate water first made its appearance. This the workmen conducted into a distinct reservoir, cut on the side of the well, on purpose for its reception; and they arched it in such a manner, that a pump might be fixed in it so as to draw this water to the surface, without allowing it to mix with any other spring which might be discovered at a still greater depth.

‘Having taken these precautions, the men proceeded to sink lower; and when they had cut through four feet more of the clay, they came to another spring, of the same nature as the former, but much stronger in its saline properties. A separate reservoir having been prepared in the side of the well for this water also, as in the former case, the men proceeded to sink to the depth of 44 feet more, in the same bed of clay, before another spring made its appearance. This water, which had then a pump fixed in it, was found to be more highly chalybeate than either of the former, and also to contain a much larger portion of common salt.’

A pair of ‘distinguished chemists’ named Brande and Park then described how the water is transported from the wells to the laboratory: ‘Several wells having been sunk to the proper depth, at one hundred feet apart from each other, horizontal borings are then made from one to the other, and half inch leaden pipes are laid in the augur holes, until they become all connected with one main well. In this a pump is fixed, and the working cylinder is placed at a sufficient depth to draw the water from all the collateral wells. Thus one pump is made to empty nine or ten wells.

‘Over each of these pumps a building is erected, to secure it from injury; and reservoirs, capable of containing one thousand gallons each, are placed among the wells, in the most convenient situations, for receiving the water. Into these reservoirs all the water from this vast collection of wells is driven by the several forcing pumps; and as these reservoirs are placed at a sufficient elevation, they empty themselves by small uninterrupted streams into a main pipe, which is conducted under ground through the fields down to the laboratory.

‘When it arrives there, the pipe is bent upwards, until it conies high enough to empty itself into a leaden cistern, of about twelve feet square, and which is placed in a convenient situation for supplying the boilers, without any further labour of bucketing or pumping, but merely by opening a stop-cock, as occasion may require.’

By 1818 there were over 70 wells – the majority of which seemingly sunk by Samuel Bendall – sending water either directly to the laboratory or via the Montpellier Spa (which had been replaced the previous year by a stone building) through several thousand feet of pipes. These wells were used for decades and some of the original wooden structures erected over the pumps were still standing 35 years later as shown in the illustration below. The cottage was lived in by the man in charge of the wells controlled by the pump housed in the tower behind.

---

The production of salts (short version)

A description of the salt making process was first published during Henry Thompson’s lifetime in The General Guide to Cheltenham by JK Griffith (1818). It is both very detailed and quite lengthy but does give a very clear picture of just what a substantial operation it was. It can be read here but those who would prefer a shorter explanation will appreciate this briefer version from the Stranger’s Guide Through Cheltenham of 1834:

‘Arrived at the manufactory, the waters are suffered to flow into large reservoirs beneath the floors, whence they are pumped up into the boilers for evaporation. This process being continued for about seven days and nights, the liquor is then drawn off into a large cistern placed in the room beneath, where it remains until the lime, magnesia, and other earthy matter has been precipitated, after which it is again pumped up into a second boiler, where, at a heat below boiling, a further concentration takes place, until the appearance of a pellicle [a thin film] upon the surface of the saline fluid gives intimation of its being in a state fit for crystallization. It is then drawn off and conveyed to the crystallizing vessels, which are deep iron pans, five feet in diameter, and lined at the bottom and in their whole circumference with marble, to prevent the salts from acquiring any stain. When these vessels are filled, a number of loose sticks are laid to float upon the surface of the liquor, for the salts to attach themselves to, that the crystallization may be distinct, and not in a confused mass, as it would otherwise he at the bottom of the coolers.

‘When the crystallization, which requires from two to five days, according to the season of the year and the state of the weather, is thought complete, the mother liquor is drawn off, and the salts show themselves in numerous beautiful clusters, covering the sticks and the whole interior of the vessels, and furnishing as beautiful an illustration of one of the finest chemical operations in nature as it is possible for the mind to conceive. The salts thus produced are now placed in square baskets to drain, preparatory to bottling, and are sold under the name of “Crystals of real Cheltenham Salts.”

‘A further process is pursued with respect to these crystals, in order to prepare them for hot climates; for though they keep very well in their original form in our own and other cold countries, yet, when exposed to the action of tropical suns, they readily dissolve. To guard against this inconvenience, therefore, the crystals are, by drying, reduced into a state of efflorescence, or powder. The room in which this process is effected is situated, over the boilers, and is heated by means of steam pipes, which travel along the shelves upon which the salts are deposited. The water of crystallization being driven off by the heat thus communicated, the rough salts soon become converted into a fine powder, which may now be exposed, with perfect impunity, to any changes of temperature, without the least chance of injury, or losing any of their valuable sanative properties. Both the crystals and the efflorescence of the real Alkaline Cheltenham Salts, contain the medicinal virtues of the No. 4 water of the wells; and can be pronounced decidedly superior to the compounds manufactured and sold by chemists as Cheltenham Salts, but which are mostly made in London. Persons who have been taking a course of the spa waters at Cheltenham, would do well upon leaving, to take some of these salts away with them; as, by occasionally taking them at their own homes, they will contribute materially to confirm that re-establishment of health, which may have been effected by the use of the natural mineral waters, which ought never to be abruptly and entirely discontinued.

‘The magnesian salts is another production obtained from the evaporation of the spa waters, and resembles in its medicinal properties the water No. 5 at the Montpellier Pump Room. By a succession of ingenious chemical operations, these salts are obtained, as a second crop, from the mother liquor, after the alkaline salts have been withdrawn. They are sold to the public as the “Efflorescence of real Magnesian Cheltenham Salts.”

‘There are yet two other preparations obtained from the mothers of the concentrated Cheltenham waters—namely, a pure magnesia, and a murio-sulphate of magnesia and iron. The former, which is of a very fine quality, is prepared and sold both in a carbonate and calcined state. The latter, from the large proportion of irony impregnations which enters into its composition, is frequently taken with great benefit in complaints requiring the aid of chalybeates and strongly tonic medicines, but it is only in such cases that it can be generally recommended; or a few grains added to the regular dose of the “real alkaline Cheltenham salts,” have often been found of essential service in improving the effects of those salts, by counteracting any weakening tendencies which, as aperients, they may perchance exercise upon very delicate constitutions.

‘All the above salts are sold in bottles, stamped with the government stamp, at prices varying from 2s. 9d. to 22s. per bottle, according to the size or the description of article required. They may be purchased at the Laboratory, the Montpellier Pump Room, or the Library adjoining, or in London at, the Depot, No. 7, Throgmorton Street.’

---

The production of salts (long version)

With some slight edits, what follows is the majority of the text concerning the salt manufacturing process prepared by ‘those distinguished chemists Messrs Brande and Parke’ as reproduced in The General Guide to Cheltenham by JK Griffith (1818). Although very lengthy, it reveals just what a substantial undertaking it was with six distinct preparations always on sale; there is also some information on the structure of the building itself (although with no surviving floor plan from this time, trying to ascertain any sort of layout is impossible).

‘The boilers employed for concentrating the waters are…made of wrought iron plates; the first boiler is nine feet long, six feet in diameter, and four and a half feet deep. The second is six feet square, and four and a half feet deep. The third is eight feet by three feet six. The three boilers, which are placed end to end in one continued row, are heated by one fire, which is placed at one end of the largest boiler, and from this the heat is communicated to the other two in succession. When these boilers are charged with the mineral water, the fire is lighted beneath them, and as soon as the evaporation has properly commenced, the cocks are partially opened which connect with the large leaden cisterns, so as to allow a small stream of the mineral water perpetually to run into the boilers, and repair the waste of fluid which the evaporation constantly occasions.

‘When the evaporation from the large boiler has been thus continued for seven days and nights uninterruptedly, amounting to not less than ninety-six gallons every hour, a large cock in the room beneath is opened, and the whole contents of the evaporating vessel is let off into a capacious cooler, in which a strainer is placed, for the purpose of arresting the carbonate of lime, magnesia, and other insoluble matter which had been precipitated from the fluid, by the operation of boiling.

‘The magnesian precipitate, which is generally very abundant, is unfit for medicinal use, in consequence of the carbonate of lime which falls with it. The proprietor, therefore, treats it with sulphuric acid, which has the property of forming a soluble salt with the magnesian earth, and an almost insoluble one with the calcareous, by which means the lime and magnesia are separated. The magnesia having thus been again brought into a state of solution, the operator draws it off by a syphon from the precipitated sulphate of lime, and carries it to the evaporating pan, where it is concentrated and prepared for crystallization. The liquor in the second boiler, when it is thought to be sufficiently concentrated, is run off and filtered in the same manner.

‘When the earthy salt has had time to subside, and the filtration is completed, which generally requires twelve hours to accomplish, the filtrated liquor is pumped up into the small boiler, No. 3, for the purpose of being farther concentrated. In this vessel the evaporation is generally continued for a week, without allowing the liquor ever to boil. At the end of this period a pellicle [a thin film] usually appears upon the surface of the saline fluid, and this is considered by the operator as a sufficient indication that the lixivium [solution] has attained that point of concentration at which it ought to be withdrawn from the boiler, and set aside for the salts to crystallize.

‘For this purpose a cock fixed in the bottom of the boiler is opened, and the whole contents let down into a large receptacle of wood placed underneath it; when the boiler is again filled as before, for a repetition of the operation. When this concentrated lixivium is removed from the boiler, it is allowed to remain undisturbed in the wooden cistern for twenty four hours, that any magnesian or calcareous earth may subside, which had not been separated by the previous filtration. The liquor, perfectly transparent, and at about the temperature of 90° is then drawn off and conveyed to the crystallizing vessel, which is a deep iron pan, five feet diameter, and lined at the bottom, and in its whole circumference, with marble, to prevent the salts from acquiring any stain. When this vessel is filled, a number of loose sticks are laid to float upon the surface of the liquor, for the salts to attach themselves to, that the crystallization may be distinct and not in a confused mass, as it would otherwise be at the bottom of the cooler.

‘When the crystallization, which requires from two to five days, according to the season of the year, and the state of the weather, is thought to be complete, the mother liquor is drawn off, and poured into a number of wooden vessels, where it remains a few days, for the purpose of procuring a second crop of crystals. The whole of the mother liquor being thus removed from the large crystallizing vessel, the salts are then taken out with appropriate shovels, and put into baskets to drain, preparatory to their being carried to the stove to be dried for sale. This first produce of the Cheltenham waters is known by the name of the “Cheltenham Alkaline Salts.”

‘(When these salts are designed for exportation to hot climates, they are deprived of their water of crystallization by the following process: They are thinly spread upon boarded sieves, in a room heated by steam, to the temperature of 80°, where they are exposed to this warm atmosphere for three or four weeks, until they have sufficiently effloresced, so as to bear being ,moved with safety to a set of wooden racks fixed over the main boilers, where they are kept in linen begs, in a temperature of 120°, till the whole of the water is abstracted. They are then ground in a mill, to be described hereafter, and when brought to the state of almost an impalpable powder, they are put up in bottles of different sizes, and sold under the name of “Effloresced Alkaline Cheltenham Salts.”)

‘When the second crop of crystals has been obtained, the mother liquor is removed to another part of the Laboratory, and poured into several iron pans set within the ground, so as for the upper edge of each to be level with the floor of the building. Here, by a long protracted evaporation, the mothers become still more concentrated, and then the muriate [compound] of soda begins to shew itself in a pellicle at the surface of the liquor, and this continues to collect, repeatedly falling as it forms, until the whole of the muriatic salt is separated.

‘As there is something curious in the construction of this apparatus, it may be worth while to describe it, before we proceed to examine the remaining processes of the Laboratory. When the proprietor found how large a quantity of steam would be produced by the salt pans, it occurred to him, that instead of letting it escape into the atmosphere, it might be applied to several useful purposes. Accordingly, the earth under a part of the Laboratory was removed, to the depth of about five feet, and the ground puddled with clay to make it hold water. A large iron pan was then fixed within this prepared bed, so as that it might be entirely surrounded with hot water; and a moveable grating was placed over it. A number of small iron pans, each three feet in diameter, were then fixed in the same bed of clay, in a long row against one of the walls of the Laboratory. The whole of these being thus fixed, small arches of brick were turned over the remaining parts of the area, for the purpose of supporting the stone floor of the Laboratory, which is laid on a level with the edges of the small iron pans just described.

‘Things being thus situated, an iron cylinder, five inches in diameter, as before mentioned, was fixed in the cover of the large salt pan, to receive the steam and conduct it under the floor of the building, for the purpose of heating the collection of iron pans already named, and producing an evaporation of whatever liquor might he put into them. In order to render it effectual for these purposes, the proprietor has contrived that a very small stream of cold water shall meet the large volume of steam exactly in the same spot at which it enters the shallow chamber, underneath the Laboratory floor; and this has the immediate effect of condensing the whole into a current of hot water. This current, which is never at a temperature below that of 190º, nearly fills the large space beneath the floor, and surrounds the whole of the iron vessels set within it; which, are just preserved at one uniform heat night and day, without any expense of fuel whatever.

”As soon as the muriate of soda has all precipitated from the mother liquor, the warm mothers are removed to a cold vessel of stone, where a pellicle of a new salt, sulphate of magnesia, soon begins to show itself, and in six or twelve hours an abundant crop of yellow magnesian sulphate, fully charged with carbonate of iron, is obtained.

‘The next object is to separate the excess of iron from the crystals of sulphate of magnesia; and to effect this, the workman dissolves them in a large portion of hot water. In this operation the oxygen of the air in the water, uniting with the black oxide of iron, converts this to the red oxide, which renders it insoluble by carbonic acid, and consequently incapable of colouring the salts in their next crystallization.

‘When the sulphate of magnesia has thus been purified from the iron, and has also been reformed by a second crystallization, it is put into baskets for the moisture to drain from it. As this species of salt is never sold from the Cheltenham Laboratory in the form of crystals, the whole of it, when dry, is carried into a set of arches formed in the stack of brick work which supports the range of large boilers: and here it sustains a heat of not less than 100º, so that in the course of a few weeks nearly the whole of the water of crystallization will be dissipated.

‘When the salt has been thus dried, it is carried to a small mill moved by water, and similar to a common corn mill. Here it is ground between two horizontal stones, and reduced to the state of an impalpable powder. It is now considered to be finished, and is sold under the name of the “Effloresced Magnesian Cheltenham Salt.”

Another salt is still contained in the mother liquor, which is the muriate of magnesia, highly charged with iron. In order to turn this to account, the proprietor dilutes it with ten times its measure of hot water and sets it aside to purify. The hot water instantly acts upon the iron, and as the iron precipitates, it carries all the other impurities down with it. In ten or twelve hours the lixivium becomes bright and nearly colourless, when it is carefully drawn off by means of a syphon, and treated with a solution of carbonate of potash for the production of carbonate of magnesia. But in order to do this in the best manner, the following measures are adopted.

‘When the alkaline lixivium is thus prepared and purified, a small portion of the solution of muriate of magnesia is put into a trial bottle, and some of the alkaline lixivium added to it by degrees, until all the magnesian earth is precipitated. This trial is made for the purpose of ascertaining not only the strength of the solution of muriated magnesia, but also that of the solution of alkali: that the workman may know how much of the carbonate of potash, any given quantity of the solution of magnesian salt will require for its complete decomposition. This having been ascertained, the clear solution of muriate of magnesia is measured into small square pans of iron lined with marble, and the appropriate quantity of the purified solution of carbonate of potash is added to it. This occasions a mutual decomposition of the two salts, and two new ones are produced, viz. muriate of potash, which remains in solution, and carbonate of magnesia which precipitates.

‘When the carbonate of magnesia has entirely subsided, the solution of muriated potash is drawn off with a syphon, and the magnesian earth is washed with several successive portions of hot water, until the last portion betrays no sign of any salt being dissolved in it. The precipitate, which is a carbonate of magnesia combined with water, is then taken out of the vessels and put upon cloth filters to drain. In 24 hours it is usually found to be sufficiently dry to be removed from the cloths, when it is taken to a warm chamber of the temperature of 106° or 107° and spread out upon shelves made of a porous sandstone, peculiarly well adapted for this purpose. Here, the cakes soon begin to lose their gelatinous appearance, and in the course of about five or six days most of the water which gave this preparation of magnesia the character of a hydrate, will have been absorbed; the carbonate of magnesia is then passed through lawn sieves to prepare it for sale.

‘When the proprietor of these works found a considerable demand for calcined magnesia as well as for the carbonate, he put up a calcining apparatus for the purpose of preparing it, which we think deserves to be described. It consists of a strong iron cylinder six feet long, with a five inch bore, and which measures in diameter, from outside to outside, 10 inches. This is fixed in brick work beneath the large salt pan, and passes directly through the fire, from which, it is defended, when not in use, by a row of fire brick. Within this cylinder the carbonate of magnesia is placed by a bent iron shovel, made on purpose for the work, and which reaches from one end of this calcining oven to the other. When it has thus been filled with the magnesian carbonate, it is closed with an iron stopper; and for farther security a round cover of wrought iron slips upon the end of the cast iron, which makes the whole completely tight. A small orifice is then opened at the other end of the cylinder for the purpose of allowing the escape of the water and carbonic acid; the fire bricks are removed from the fire place, and the calcination commences.— In about three hours the operation is finished, and every twelve pounds of carbonate produces six pounds of calcined magnesia. When the calcination is finished, if it is not intended to repeat the process, the fire-bricks are immediately replaced to preserve the cylinder from the destructive action of the fire at the time when the calcination of magnesia is not going on.’

---

^{We are grateful to Roger Beacham for originally providing a copy of the 1809 Treatise on Cheltenham Waters and to Jill Waller for sharing her research on Thompson’s wells and providing the illustration of the Pumpers Cottage.}

TO READ ABOUT SALTS FROM 1856-1899 CLICK HERE