THE ART OF MAKING COMMON SALT.
PARTICULARLY ADAPTED TO THE USE OF THE AMERICAN COLONIES WITH An EXTRACT from Dr. BROWNRIGG'S Treatise on the Art of making BAY-SALT.
Detached from the Pennsylvania Magazine for March 1776.
PHILADELPHIA: Printed by R. AITKEN, Printer and Bookseller, opposite the London Coffee-House, Front-Street. M.DCC.LXXVI.
THE ART of making COMMON SALT.
THE French marshes, in which immense quantities of salt are annually made, are contrived in a much more artful manner; and as they are the most commodious that have hitherto been invented, it may be proper here to transcribe an account of them, as given by an ingenious French physician, and published in the transactions of Royal Society.
Explanation of the Plate.
A A A is the sea.
1. 1. The entry by which the sea water passes into B B.
B B, the first receptacle, in which the water maketh three turnings as you see, and is ten inches deep.
2. 2. The opening by which the first and second receptacle have communication one with another.
E E F, The third receptacle is properly called the marsh.
d d d d, is a channel very narrow, through which the water must pass, before it enters into the third from the second receptacle.
3. 3. is the opening by which the water runs out of the second into the third receptacle. The pricks you see in the water throughout the whole scheme, do mark the course and turnings which the water is forced to make, before it comes to h, h, h, h, which are the places where the salt is made.
h, h, h, h, are the beds of the marsh, where the salt is made, and in them the water must not be above an inch and an half deep; each of these beds is fifteen feet long, and fourteen feet wide, and framed on every side with wood.
8. 8. 8. 8. are the apertures by which the beds receive the seawater, after may windings and turnings.
9. 9. 9. 9. are the little channels between the beds.
When it rains the openings 2. 2, 3. 3. are stopped to hinder the water from running into the marsh. Unless it rains much, the rain water doth little hurt to the marsh; the heat of the sun sufficiently exhaling it, if it be not above an inch high: only if it have rained very plentifully that day, no salt is drawn for the three or four days next; but if it rain five or six days, the people are then necessitated to let all the water out of the beds by a peculiar channel, which cannot be opened but when it is low water. But it is very seldom that it rains so long as to constrain men to empty those beds. The hottest years make the most salt, and in the hottest part of the summer, there is salt made even during night. Less salt in calm than in windy weather.
The west and north-west winds are the best for this purpose.
Our country people draw the salt every other day, and every time more than an hundred pound weight of salt.
The instruments used to draw the salt have many small holes to let the water pass, and to retain nothing but the salt.
The reddish earth in the marshes make the salt more grey, the bluish more white. Besides, if you let run in a little more water than you ought, the salt becomes then more white, but then it yields not so much. Generally all the marshes require a fat earth, neither springy nor sandy.
[Page 4] The salt man who draws the salt must be very dextrous. In this isle of Rhee, men there are that draw very dark salt, and others that draw it as white as snow, and so it is at Xaintonge. Chiefly care is to be taken that the earth at the bottom of the beds mingle not with the salt
The salt we use at our tables is perfectly white, being the cream (or that salt which is formed on the top of the water) drawn four or five hours before the salt is to be drawn. The grains of it are smaller than of the other. Generally the salt of Xaintonge is somewhat whiter than ours. The bigness of our salt is the size of a pepper grain, and of a cubical shape,
The marshes are preserved from one year to another by overflowing them a foot high.
The timber of the marshes, if it be of good oak, keeps near thirty years; but there is used but little wood, all the ditches and apertures being done with stone.
The foregoing description being in some parts obscure and in others imperfect, it is necessary to add to it a few remarks by way of explanation, that the construction of the French salt marsh, and the method of preparing salt therein, may be better understood. And this seems to be the more necessary, since although the above account of the French method of making salt hath long been published, yet it hath not been brought into use, neither in Great Britain, nor in the British colonies in America.
These, therefore, who would make a salt marsh, commonly chuse a low plot of ground adjoining to the sea, distant from the mouths of large rivers, but nigh a convenient harbour for boats or larger vessels: This ground must be free from springs of fresh water, and no ways subject to land floods, and if possible should have a clayey bottom; it should also be defended from the sea either by banks of rising ground, or by an artificial mole raised for that purpose.
The ground so chosen must be hollowed out into three ponds or receptacles: The first into which the sea water is usually admitted, may be called the Reservoir; the second receptacle (which is divided into three distinct ponds communicating with each other by narrow passages, and containing brine of different degrees of strength) may be called the Brine-ponds; the third receptacle is furnished with an entrance, between which and the brine-ponds, there runs a long, winding narrow channel, the rest of it is divided into several shallow pits, containing a fully saturated brine, which in them is converted into salt, and may therefore be distinguished by the name of the Salt-pits.
The first receptacle or reservoir, must have a communication with the sea by a ditch defended on each side with walls of brick or stone, and made of such a depth that by it all the water contained in the reservoir and other parts of the salt marsh, may flow out at low water; and by it also the sea water may be admitted into the reservoir at full sea; so that at neap tides the marsh may be filled with sea water to the depth of two feet, when there is occasion to overflow the marsh, as is done in the winter season, when no salt is made: By which means the wood work is longer preserved from decay, and the bottom of the marsh from frost [Page 5] and other injuries. And in order that the marsh may be thus overflowed when occasion requires, it is necessary that the several receptacles should be sunk so deep that the ground on all sides may be sufficiently alerated to keep in the sea water, at the depth above mentioned. The ditch between the sea and the reservoir must also be provided with a sluice or floodgate, by which the sea water may be admitted, retained, let out, and the whole salt-marsh drained, as occasion may require.
The several ponds or receptacles must not have their bottoms all upon the same level, but must be made of unequal depths, so that the first receptacle or reservoir must be 8 1-2 inches deeper than the salt pits in the third receptacle; the three brine ponds situated between the reservoir and the salt pits, must also be of unequal depths, that adjoining to the reservoir being the deepest, and that which is nighest the salt pitts the shallowest, but all of them must be shallower than the reservoir; and the three receptacles being thus constructed, the water standing at the same heighth in them all, and forming by its surface one continued plain, will be ten inches deep in the reservoir, when only one inch and an half in the salt pits.
The judicious French author hath not given us any account of the length and breadth of the reservoir and brine ponds, but some judgment may be formed of their size from his plan of the whole work. It will be better to err by making them too large than too small. In general, they ought to be large enough to furnish the salt pits with a constant supply of brine, fully saturated with salt; and for that purpose it is necessary to have them of different dimensions in different countries, as will be hereafter explained.
It is not necessary that the reservoir should be exactly of the form which the French author hath described, where the ground will admit of another that may be chosen; and even the brine ponds and salt pits may be made of different forms, if due regard be had to the general contrivance of the whole work.
For the bottoms of the reservoir and brine ponds, any kind of tough clay or earth, that will hold water, may serve very well. The French make the bottoms of their salt pits of any blue or red clay they meet with; but in order to have a white clean salt, it is necessary that those pits should be carefully laid with some strong cement, that will retain the brine and cannot easily be broken up. As to the other particulars relating to the structure of the French salt marsh, they are sufficiently explained by the ingenious physician whose account is before inserted.
The marsh being thus constructed, the salt-men at the proper season of the year, open the floodgate when the tide is out, and drain off all the stagnating water, and if there be occasion repair the bottom of the marsh, and cleanse the several receptacles from mud and dirt. Afterwards when the tide rises, they by the same floodgate admit the salt water into the marsh, till it stands in the reservoir at the height of ten inches. In a day or two most of the water in the saltpits is exhaled, and what remains in them is a very strong brine. They then let in more sea water, and so take care every two or three [Page 6] tides (oftener or seldomer as occasion requires) to admit as much water into the reservoir, as will supply the place of that which hath been wasted in vapours, constantly raising it to the heigth of ten inches in the reservoir, and consequently to an inch and a half in the salt pits; all the parts of the marsh are thus supplied with water out of the reservoir; but the sea water which flows into the reservoir is not confusedly mixed with the salt-water contained in the other parts of the works; for as the several parts communicate only by narrow passages, it is provided that the salt water flowing out of the reservoir never returns there again, but gently flows along till it arrives at the second brine pond, and afterwards at the third, being forced forward by the sea water from time to time received into the reservoir. During this slow course, the watry fluid continually flies off in exhalations, and the brine is continually preparing for chrystallization as it gently flows along, growing stronger and stronger the nearer it approaches the salt pits; so that when it enters these pits it is fully saturated with salt, and particular care is taken to guard the enterance of the salt-pits with a long winding narrow channel, by which means the strong pickle contained in these pits is prevented from returning back and mixing with the weaker brine in the brine ponds; care is also taken that the strong pickle in the salt pits be spread out very thin to the sun and air with a large surface; by which means the watery vapours more quickly exhale from it, leaving the salt concreted into chrystals. These the salt-men carefully draw out, and oftentimes dispose into large pyramidal heaps, which they thatch over with straw, and so preserve them from the injuries of the weather. Thus, at a small expence and trouble, a salt is prepared which is found extremely fit for all domestic uses: and thus France is also furnished with a very profitable article for exportation into foreign countries.
The French have so many works of this kind that an ingenious author of that nation affirms, that in favourable seasons, as much salt is sometimes made in a fortnight, as is sufficient for the annual consumption of that kingdom, and of all those other nations who purchase much more of it than the French consume themselves; but after a rainy summer there is often a scarcity of salt, and the price of it increases.
By attending to the foregoing extract, it appears sufficiently evident, that bay salt may be made in any of the United Colonies, especially the more southern ones. Dr. Brownrigg has given us the method of making it in France; by the description of which it appears, that the grand principle of the operation is to throw the sea water into a large surface, and thereby cause the watery parts to be speedily evaporated by the sun and air. An ingenious operator may apply this principle in many methods different from that above described, and perhaps in some that may be more profitable. In some cold countries, the Dr. saith, where fuel is dear, they first raise water, not near so salt as rain water, to the height of twenty or thirty feet by a pump, and thence let it run down over bundles of sticks, under a roof, but exposed to the air and sun, and by the time it comes to [Page 7] the bottom it is exceeding salt, and then they boil it to salt with little expence of fuel. If the water was pumped in some such manner, only without a roof, into the first receptacle, it would doubtless accelerate the evaporation.
The Dr. in a proposal to have bay salt made in England, considering the slowness of the evaporation in that climate, and the heavy rains that often fall, proposes to have covers of thin boards, or canvas painted white and stretched on frames to cover the salt-pit when it rains, and when the sun shines to raise them on hinges nearly perpendicular, fronting to the south, with a space between their bottom and the ground of a foot wide, for the air to pass thro'; by means of which, and the reflection of the sun, a strong evaporation must take place. When they cover the salt pits with these boards or canvas to keep off the rain, they also stop the passages to them, to prevent the rain water which may fall in the other receptacles from getting into them, and if a heavy rain should fall so as to render the water in the the receptacles weaker than sea water, it may be best to draw it off, otherwise not. Those who are acquainted with the exceeding quick evaporation of water in our summer months, especially in the middle and southern colonies, will judge whether the advantage of such additional machinery will compensate the expence. If a fortnight's seasonable weather is sufficient in any part of France to supply that large kingdom with salt for its own consumption, and as much more for exportation, we can hardly doubt whether the United Colonies can produce their own salt, by the natural evaporation of the sun and air.
In some climates where the natural evaporation is not a sufficient over-balance for the rains that fall, they produce their salt by boiling the water, and this is called white salt, or boiled salt. The apparatus for this process is expensive, and the consumption of fuel great, and without skill in the operation, the salt produced is much inferior to bay salt, as it will not be so strong, and will retain a certain calcarious or limey earth very prejudicial to meat, and also a certain liquor called Bittern: both which, the Dr. saith, are in a good measure avoided in the natural process of making bay salt. The design of this publication being to promote the making bay salt, no particular description is given of the making white or boiled salt. Perhaps it may be best to prosecute both methods; but the preparation for boiling salt being so much greater, it may be best to begin with making bay salt, as it comes within the the compass of more peoples ability.
The making salt in America has been an object of attention to many persons in Britain for a long while past, arising from the favourableness of our climate to the operation. It has been too long neglected, from a prevailing disposition in the Americans to manufacture nothing among themselves, which could be imported from abroad: But it is now reasonably to be expected, that the necessity of America will induce the inhabitants, among many other useful manufactures, to establish that essential one of making into salt the sea water that washes their shores.