Transactions of the Geological Society, 1st series, vol. 2/On the Brine Springs at Droitwich
By Leonard Horner, F.R.S. M.G.S.
§ 1. THE town of Droitwich is situated nearly in the centre of Worcestershire, about six miles from Worcester, on the road to Birmingham. For a very long time the manufacture of salt has been carried on to a great extent in this place, and as I am not aware of the existence of any detailed account of the natural and chemical history of the brine springs from which it is procured, I take the liberty of laying before the Society some observations which I made on the spot in October, 1810, together with the results of some experiments I have since made, with the view of determining the chemical composition of the brine.
§ 2. The brine-pits are in the centre of the town, situated in a narrow valley, in the bottom of which runs the small river Salwarp. The sides of the valley rise rather abruptly from the river. Doder Hill, on the right bank, which appeared to me to be the highest of the two sides, I measured with the barometer, and found it to be about eighty feet above the bed of the river.
§ 3. The prevailing rock around Droitwich is a fine-grained calcareo-argillaceous sandstone, of a brownish red colour, with occasional patches and spots which are greenish blue. At Doder Hill, where a vertical section of it is exposed, it contains beds of a greenish grey colour, and of a more indurated texture, but which do not appear to differ materially in composition from the red sandstone. These contain slender veins of crystallized gypsum, the forms of which are very distinct, where the widening of the vein has produced small cavities. I did not observe any gypsum in the red sandstone. The stratification is horizontal, and both the red and the grey rocks, where they are exposed to the air, crumble down into small pieces. I did not discover any traces of organic remains.
This sandstone is the same as that which Mr. Aikin has described as occurring to so great an extent in Shropshire and Staffordshire, and which he considers to be the old red sandstone of Werner. He has also stated that it is found in this district, but as he does not trace it to any particular spot beyond Droitwich, I may here observe, that it appears to me to be the same as that which I found on the banks of the Severn, between twelve and thirteen miles from this place; and I have great reason to believe that it continues without interruption throughout the whole of that extent, and even for some miles to the south of the spot I have just named.
Mr. Aikin observes that the red sandstone of Shropshire does not effervesce with acids: in this respect, therefore, it differs from that of Droitwich, for both varieties of the sandstone effervesce pretty briskly for a short time, but that which is of a grey colour appears to contain the greatest proportion of calcareous matter.
The extensive beds of rock-salt, and the brine-springs of Cheshire, according to Dr. Holland, are situated in strata of a similar nature.
§ 4. The surface soil which covers the red sandstone, contains large pebbles, generally about the size and shape of a goose's egg, but often larger. Those which I examined consisted of compact bluish grey quartz, very much resembling some varieties of flint and chalcedony, and different varieties of coarse and fine-grained quartzose sandstones. These pebbles are not found in great quantity, for, as I was informed by a labourer, they are picked off the surface of the fields for the purpose of mending the roads, no spot having been found in the neighbourhood, where they are sufficiently abundant to pay the expence of digging for them.
§ 5. With regard to the nature of the rocks through which the brine-pits were sunk, I have not been able to obtain any very distinct information, as no new pit has been made for the last thirty years. All that I have in my power to lay before the Society on this subject, is the account contained in Nash's History of Worcestershire, together with some details I received from an inhabitant of Droitwich, who was on the spot at the time the last pit was dug. The following is the information given by Dr. Nash.
“Until 1725 the pits had not been sunk very deep, but in that year the talc was sunk through, and soon after every one sunk his pit through the talc, and obtained such a profusion of strong brine that not one-tenth part of it hath ever been used, but ran to waste. In 1773 Joseph Priddey, of Droitwich, informed me that he had sunk several pits, and generally found it about 35 feet to the talc, through the stratum of talc 150 feet, under the talc a river of brine 22 inches deep, under this river a hard rock of salt. When the hole is bored through the talc, the brine bursts up with amazing violence to the surface of the ground. In the year 1774 he sunk another pit, and found it to the talc 53 feet, through the talc 102 feet, the brine river 22 inches, then a rock of salt: he bored 21 feet into this rock, and found it still the same. In 1779 a hole was bored previous so a brine pit being sunk in the yard of Richard Norris, Esq. The strata were, mould 5 feet, marl 35, talc 40, a river of brine 22 inches; under the brine, talc 75 feet, and a rock of salt, into which the workmen bored 5 feet. I have been informed, likewise, by persons employed in sinking these pits, that immediately above the river of brine is a thin crust, easily perforated, and, next to that, a very soft substance, perhaps two feet thick, and then the talc. This talc, or rather gypsum, or alabaster, is a shining fissile species of stone, of a whitish colour. It is so hard that the workmen never sink the pit through it; they bore a hole, four inches in diameter, through which the brine rises and fills the pit.”
I was informed by an old man who assisted in sinking Walker's pit, that they sunk through soil, gravel, red marly clay, blue and white stone, hard rock, and talc, and that they came to the brine at the depth of 50 yards from the surface; that for the first 15 yards they cut out a shaft, about 8 feet square, this they coated with clay, and afterwards lined with planks, to prevent the springs of fresh water, which are found at that depth, from mixing with the brine. At this depth of 15 yards they found the hard rock, and they then bored a hole of about 4 inches in diameter through this hard rock until they came to the brine, which they found at the depth of 35 yards farther; when they came to the brine, the borer suddenly fell 22 inches, thus indicating the depth of it. As soon as the rock was penetrated, the brine rushed rapidly through the hole, the mouth of which the workmen were obliged to stop, until they got out of the pit. When the plug was withdrawn, the brine quickly rose to the surface and overflowed.
§ 6. Although the information contained in the preceding statements is not very precise, yet they convey a general idea of the nature of the rocks sunk through, and it is very probable that they are similar to those exposed at Doder Hill, immediately contiguous to the pits, and which I have already described. We learn, however, with tolerable certainty, that these springs are impregnated from a body of rock salt; and we obtain an additional testimony in support of the observation, that rock salt is invariably accompanied by gypsum. From the rapidity with which the brine rises to the surface, it is evident that the source of these springs must be situated in much higher ground than that in which the pits are sunk.
§ 7. There are several pits on both sides of the river, but chiefly on the south side. The greater number of them, however, are not used, and the whole of the present extensive works are supplied from four pits. Indeed, the quantity of brine that is used bears but a small proportion to that which is allowed to run to waste; for, except when the reservoirs are filling, the brine is constantly flowing into the adjoining canal, through a channel cut for the purpose, near the mouth of the pits.
§ 8. The four pits that are worked at this time are distinguished by the names of Walker's Pit, Walwyn's Pit, Romney's Pit, and Stuckey's Pit. From each of these I obtained a bottle of the brine, for the purpose of submitting it to chemical examination. I also procured a bottle of the brine from Farley's Pit, on the north bank of the river, but which is not now worked.
I shall now lay before the Society the details of the process I adopted in this analysis.
§ 9. The brine from all the pits is perfectly limpid, and when held in a tumbler is colourless; a greater body of it, however, has a pale greenish hue, similar to that of sea-water. It has remained equally clear at the end of a year and a half in a bottle closely corked, and no change of transparency was produced, when left exposed to the air in an open vessel, for several days.
Its taste is intensely saline, but without any degree of bitterness; neither is there any bitter taste in the crust which is deposited at the bottom of the pans, after several successive portions of brine have been evaporated.
The temperature of the brine in the pits, a few feet below the surface, differed very little from that of springs in general. It was 55°.
The specific gravity of the several brines I found to be as follows:
|Walker's pit,||317.14||grs.||= 2289.75||grs. in a pint.|
|Walwyn's pit,||313.40||= 2262.75|
|Romney's pit,||311.00||= 2245.42|
|Stuchey's pit,||283.50||= 2046.87|
|Farley's pit,||266.34||= 1922.97|
This variation in the strength of the different brines is probably owing to the mixture of the fresh-water springs in different proportions. Farley's pit, which is the weakest, is perhaps so on account of the brine not being agitated by pumping, whereby the lighter fresh water will only mix with the brine in the upper part of the pit: the bottle of it which I obtained was from near the surface.
a. Tincture of red cabbage—no change produced.
b. Litmus paper—no change.
c. Turmeric paper—no change.
d. Lime water—no change.
e. Nitrate of barytes—a considerable white precipitate.
f. Oxalate of ammonia—a white precipitate.
g. Ammonia—a slight turbidness.
was separated by filtration, and on the addition of phosphate of soda to the clear liquor, a slight turbidness was produced, and, after a little time, a rod drawn along the glass vesselleft white streaks.
i. Succinate of ammonia—no change.
k Tincture of galls, a turbidness, but no blackness.
The brine, therefore, does not contain any uncombined acid, (by Exp. a. b. d.) nor uncombined or carbonated alkali, (by Exp. a. c.) nor earthy carbonate or oxide of iron, (by Exp. m.) nor iron in any other state of combination, (by Exp. i. k. l.)
As a farther proof that it does not contain either an earthy carbonate, or oxide of iron, the crust left at the bottom of the pan
after the evaporation of successive portions of the brine, called by the workmen pickings, and of which I procured specimens, is entirely soluble in water.
The brine appears to contain, besides muriate of soda,
1. A sulphate, or sulphates, (by Exp. c.]
2. Lime, (by Exp. f.)
3. Magnesia, (by Exp. g. h.)
The sulphuric acid may be in combination either with lime, magnesia, or soda, or with all the three.
The lime and magnesia may be in combination either with sulphuric or muriatic acid, or with both.
§ 12. These preliminary experiments were made upon the brine from the live different pits; and as all the specimens gave the same results, I considered it only necessary to determine the proportions of the several ingredients in one of them. I employed for this purpose the brine from Walker's pit, as being the strongest.
From one ounce measure of brine weighing 542.8 grs. I precipitated the sulphuric acid by nitrate of barytes, separated the precipitate, and washed it with distilled water, until no change was produced in the washings by nitrate of silver, and taking care to add all these washings to the brine. I now precipitated the muriatic acid by nitrate of silver, which last I added in excess. The muriate of silver was washed with distilled water until no change was produced in the washing by muriate of soda. It was then dried in a low sand heat over a lamp, until it became of a purple hue throughout. It now weighed 339.63 grs. which is equal to 64.7 grs. of acid, taking the composition of muriate of silver to be 19.05 acid and 80.95 base, according to the determination of Dr. Marcet, and which, from its close coincidence with that of Gay Lussac, appears most entitled to confidence.
a. Three ounce measures of the brine, weighing 1628.4 grs. were evaporated to dryness in a heat not exceeding 200°, and which was reduced to 180° towards the close of the operation. The residuum was reduced to powder, and again exposed to a heat of about 180° until no farther moisture was given off. It now weighed 431.86 grs.
b. This residuum finely powdered, I put into a flask, and poured on it two ounce measures of alcohol nearly boiling. It stood forty eight hours, during which time it was frequently shaken. It was then filtered, and the salt left on the filter was washed with two ounces of fresh hot alcohol.
c. The filtered liquor was evaporated to dryness in a very gentle heat, and a small quantity of fresh alcohol was added to the residuum, to separate the earthy muriates from the muriate of soda taken up by the alcohol in the process b. This was filtered, and the liquor being evaporated to dryness yielded 0.32 gr. of residuum.
d. This residuum was dissolved in distilled water, and as it was unnecessary to attempt to ascertain the proportions of muriate of lime and muriate of magnesia in so small a quantity, supposing them both to be contained, all I could do was to determine the existence of each.
e. To one portion of this solution I added oxalate of ammonia, which produced no change.
f. To another portion I added pure ammonia, which immediately occasioned a flocculent precipitate.
g. To a third portion I added neutral carbonate of ammonia and phosphate of soda; a precipitate was produced, and a rod drawn along the glass left white streaks.
The whole therefore of this residuum was muriate of magnesia, with perhaps a minute quantity of muriate of soda.
a. To three ounce measures of brine, weighing 1628.4 grs. I added nitrate of barytes in excess. The precipitate was well washed, dried over a lamp, and afterwards heated to redness in a platina crucible. It weighed 22. grs. which is equal to 7.37 grs. of acid, or 2.46 grs. in an ounce; according to the proportions of Berthollet, of 33.5 acid and 66.5 base in 100 parts of sulphate of barytes.
This acid might either be combined with lime, magnesia, or soda, or with all the three. To determine what it was combined with, I dissolved the salt which had been freed from the earthy muriates by the process B. b. in distilled water.
b. To this solution I added oxalate of ammonia in excess: the precipitate after being well washed, and dried in a heat not exceeding 165°, weighed 5.68 grs. which is equal to 2.01 grs. of lime, or 0.67 gr. in an ounce, according to the proportions of Dr. Thomson of 35.5 of lime in 100 parts of the oxalate.
c. To the clear solution from which the lime had been thrown down, I added ammonia, and as it produced no change I concluded that no sulphate of magnesia exists in the brine.
But as 2.01 grs. of lime will only take up 2.9 grs. of sulphuric acid, I infer that the remaining 4.47 grs. of acid must be combined with soda.
1. By Exp. A. it has been shown that one ounce measure of the brine contains 64.7 grs. of muriatic acid, and as by Exp. B. c. it has been shewn that there is no muriate of lime, the whole of this muriatic acid must be in combination with soda, with the exception of the small quantity of muriate of magnesia found by Exp. B. f. g. Muriate of magnesia, according to Dr. Marcet, contains 56.01 per cent. of acid, therefore deducting 0.18 gr. for the acid contained in the 0.32 gr. of muriate of magnesia obtained in Exp. B. from three ounces of the brine, or 0.06 for that contained in one ounce, there will remain 64.64 grs. of muriatic acid, which is equal to 140.52 grs. of muriate of soda in one ounce of the brine, according to the proportions of Dr. Marcet of 46 acid and 54 soda in 100 parts of salt.
2. By experiment C. b. it has been shewn that three ounces of brine yielded 5.68 grs. of oxalate of lime, dried at 165°; and by Exp. C. a. and B. c. the lime has been shewn to be in combination with sulphuric acid: 5.68 grains of oxalate of lime, according to Dr. Henry, are equal to 7.1 grs. of sulphate of lime, both salts being dried at 160°: there are therefore 2.37 grs. of sulphate of lime in one ounce of the brine.
3. From the several experiments made with the view of determining the amount and nature of the sulphates, it has been inferred that there are 4.47 grs. of sulphuric acid in combination with soda in three ounces of the brine, which, (according to the proportions of Kirwan of 25.52 acid, 18.48 soda, and 58 water,) are equal to 7.98 grs. of dry sulphate of soda, or 2.66 in one ounce.
4. By Exp. B. it has been shewn that there are 0.32 gr. of muriate of magnesia in three ounces of the brine or 0.11 in one ounce.
Therefore the several salts contained in the ounce of the brine consist of
|1. Muriate of soda||140.52||grs.||=||2248.82||grs. in a pint.|
|2. Sulphate of lime||2.37||=||37.92|
|3. Sulphate of soda||2.65||=||42.40|
|4. Muriate of magnesia.||0.11||=||1.76|
|Or||Muriate of soda||96.48||per cent.|
|Sulphate of lime||1.63|
|Sulphate of soda.||1.82|
|Muriate of magnesia||0.07|
By Exp. B. a. it has been shewn that three ounces of the brine yielded by evaporation 431.86 grs. of entire salt, which is equal to 143.95 grs. in one ounce.
Before concluding this paper, I shall compare the results I have obtained, with the accounts of the Cheshire Brine Springs, given by Dr. Holland in his Agricultural Survey of that county, and subsequently by Dr. Henry in the Philosophical Transactions for 1810.
The densities of the different brines in Cheshire and at Droitwich are very nearly alike. In general, the former seem to contain rather a larger proportion of pure muriate of soda. The Droitwich brine is free from carbonate of lime, oxide of iron, and muriate of lime; all which are contained in that of Cheshire, though in very minute quantity. But the most remarkable difference between the two is, that the brine of Cheshire contains no sulphate of soda, which I have found in that of Droitwich, in the proportion of nearly 2 per cent.
I was disposed to doubt the accuracy of my experiments, until I found that Nicolas, in his memoir “Sur les Salines des Departemens de la Meurthe, du Jura, du Doubs, & du Mont,” Hassenfratz in his memoir ”Sur le Sel Marin”, and Montigny in his memoir “Sur les Salines de Franche Comté,” state sulphate of soda as a constituent part of all the brine springs they examined. There is therefore no reason why this salt should not exist in the brine at Droitwich; especially as it is one so commonly met with in mineral waters.
It is foreign to the object of this paper to describe the process adopted in the manufacture of salt at Droitwich. It does not differ in any material respect from that employed in Cheshire, of which Dr. Holland has already laid before the public a very full account in his excellent work already alluded to.
- In 816, Kenulph, King of the Mercians, gave Hamilton and ten houses in Wick, with salt furnaces, to the church of Worcester.
“At the time of Domesday Survey,” which was finished in 1087, “the only fuel used for boiling the brine was wood, and the demand for it much greater than the neighbourhood of Droitwich could supply, especially as the brine was of a weaker quality in those days, and required to be boiled longer than it does at present.”—Nash's History of Worcestershire.
- In the Philosophical Transactions for 1678, there is a short account of the saltworks of Droitwich by Dr. Thomas Rastel. At that time there were three pits made use of, the greatest of which was thirty feet deep. He found that the brine yielded above one-fourth of its weight of salt.
- Dr. Rastel says, “I never observed any shells”─Phil. Trans.
- Trans. of the Geol. Society, vol. I, p. 191.
- Trans. of the Geol. Society, vol. I, p. 312.
- Trans. of the Geol. Society, vol. 1, p. 38─See also his Agricultural Survey of Cheshire.
- The account of the sinking of this pit differs so materially from the rest, that I suspect it must be inaccurate. In the accounts of the sinking of the other pits, the brine flows over rock-salt; but here 75 feet of gypsum intervene between the brine and the salt. As all the pits are situated within the space of a square furlong, it is not probable that so remarkable a change should take place in the relative position of the gypsum and the rock salt.
- In different places in the town of Droitwich, the water in the wells is brackish, while in others, that are sunk to the same depth, it is quite fresh.
- Through the kindness of Thomas Farley, Esq. the principal proprietor of these works, I have learned, that the quantity of salt, annually made at Droitwich, is about 16,000 tons.—The principal part of this is consumed in England, and pays a duty of about £320,000.—The present market price of the salt is £31 per ton, £30 of which is duty.
- I omitted to note down the temperature of the air, but it was a warm day for the season of the year.
- This is not an absolutely saturated solution, for by adding salt to the brine at a boiling heat, and allowing it to cool to 60°, I obtained a perfectly limpid solution of the specific gravity of 1210.39. This sp. gr. almost exactly corresponds with that of Hassenfratz, An. de Chemie. vol. 28, p. 298. In the sixtieth volume of the Philosophical Trans. Dr. Watson, the present Bishop of Llandaff, has given a valuable paper, entitled, “Experiments and Observations on various Phenomena attending the Solution of SaIts.”─He has constructed a table of the specific gravity of water impregnated with different quantities of common salt, from 1 down to the 1024th part of the weight of the water, at a mean temperature of 50°. The salt used was sea-salt, of the finest kind, and extremely dry.
The highest specific gravity which he gives, is 1206, which very nearly corresponds with that of Walker's pit; but from what has been said above this is not the specific gravity of a fully saturated solution.
But a solution of this specific gravity he states to contain 1 of its weight of salt; whereas I have found (B. a.) that three ounces of the brine of Walker's pit, weighing 16284 grs. yielded only 431,86 grs. of salt, which is not equal to two-sevenths of the weight.
The difference between the results which I have obtained, and Dr. Watson's tables, (if it is not owing to error on my part,) may probably arise from the degree of purity of the salt which he used, and also from the state of it with regard to dryness, before it was added to the water.
Dr. Holland, in his Agricultural Report of Cheshire, states, that salt, after as much water as possible has been previously drained from it, loses about one-seventh of its weight, when heated and dried before the fire, without being allowed to decrepitate.
- This experiment was made on the spot.
- This turbidness was evidently owing to the alcohol of the tincture.
- As all the other salts, besides the muriate of soda, were shewn by the preliminary experiments to exist in comparatively small quantities, I used a larger proportion of the brine in the determination of these, to avoid as much as possible the errors of too minute manipulations.
- So that the brine contains 26.53 per cent. of salt.
- Memoires d'Arcueil, vol. ii.
- Henry's Elements of Chemistry, sixth edition, vol. ii. page 141.
- Analysis of the Dead Sea, Phil. Trans. 1807.
- Phil. Trans. 1810.
- I calculate the sulphate of soda in the dry state, because in the estimate of the quantity of entire salt, in the brine (with which the gross amount of the several ingredients obtained separately will be compared) the residuum was dried in a heat sufficient to drive off the water from the sulphate of soda. To prove this, I exposed 152 grs. of the entire salt which had been dried in the same way, to a strong red heat in a platina crucible, and there was only a loss of about 3ths of a grain, and that loss must have arisen from the water that would be separated from the sulphate of lime.
- This excess in the amount of salt obtained by the estimate of the several ingredients, may probably arise from the difficulty of drying the different salts to the precise point implied in those experiments by which the proportions of their coefficient parts have been determined.
- I have already stated, § 10. that there are 2289.75 grs. of entire salt in a pint of the brine from Walker's pit. In estimating that quantity, I made use of a cubic inch measure, whereas in the other case (by inadvertence) an ounce measure was employed. The difficulty of measuring the quantity very accurately in both cases is very great, and in a saturated solution, au imperceptible variation in bulk would become very sensible in weight.
- Annales de Chimie, vol. 20.
- Annales de Chimie, vol. 11.
- Memoires de l'Academie des Sciences, 1762.