Salt and the salt industry

by Albert Frederick Calvert

CHAPTER VII
LATEST METHODS OF SALT-MAKING

In tracing the development of the salt-making industry in this country, it will be observed that, until the last quarter of a century, the old open-pan system defied improvement, and the salt-makers from generation to generation successfully resisted the endeavours of all who suggested innovations or hinted that better methods could be introduced in the manufacture. It is true that experiments were made with the sizes and arrangement of the pans, that coal replaced wood and straw as fuel, that the locomotive superseded the wain as a means of transporting salt from the works to the markets, and that pumps were employed instead of buckets to raise the brine and deposit it in the cisterns which supplied the pans; but these several developments produced no change in the system of manufacture, which consisted of lighting a fire beneath a pan of brine, driving off the water in the form of vapour, and collecting the salt crystals that form and sink to the bottom of the pan. The salt-men were devoted to their primitive, rule-of-thumb methods, and the most enterprising among them regarded the process as unimprovable. In the construction of salt-works there was no attempt at engineering exactness; the size of the pans was regulated roughly by the dimensions of the plates of which they were made; and the heights of the brickwork of the furnaces, etc., was usually reckoned by courses of bricks.

The fireman, the real salt-maker, whose business it was to attend to the fires and see that the proper degree of heat was maintained to produce the variety of salt required, did his work almost entirely by rule-of-thumb. It was only rarely that a thermometer was used. The technical knowledge acquired by experience enabled a man to see at a glance whether the pan was working properly, and the quantity and quality of the salt showed whether his work had been well or ill done. The late Thomas Ward was a greatly respected authority, one of the most reliable experts of the Salt Union, and a voluminous writer and indefatigable lecturer on every aspect of the subject of salt, but he failed to persuade himself that it was even thinkable that the open-pan system should ever be abandoned in favour of a more scientific, more rapid, or more economical process.

Mr. Ward admitted that the process was archaic, but he was at pains to demonstrate that the trade was justified in desiring it to remain so. He argued that the price of salt was so low, and the product was so bulky, that costly and elaborate apparatus was both inappropriate and ineffective. He compared the life of an ordinary open salt-pan with that of any of the innumerable patented pans that had been tried, and found that the ancient article produced salt at less cost than the patent contraptions, and was far easier to repair. “The chief business of the salt manufacturer,” Mr. Ward wrote in 1894, “is to utilize to the best purpose, for the production of salt, the heat obtained from the fuel. To this end, innumerable patents have been taken out, but few have been so successful as the simple application of direct heat to open pans. The method seems a very primitive one, and most visitors to salt-works think they can improve upon what they consider a rude, antiquated system. I have had brought before me, and have seen working, scores of patented plans. In all, or nearly all, the idea was to economize heat; and if the whole of salt manufacturing consisted in evaporating the greatest quantity of water with the least quantity of fuel, doubtless many of the schemes would succeed instead of fail, as they do now.”

Since the open-pan system of manufacturing salt from brine was in general and uninterrupted use in this country from the time of Julius Caesar to within a few years ago, we must study the interim developments from direct-fire to vacuum pan evaporation in the industry of the State of New York. The salt springs in New York State were discovered by Jesuit missionaries about the middle of the seventeenth century, but the manufacture of salt on a commercial scale was not begun until 1788, when the industry was established in the vicinity of Syracuse. Solar salt is still manufactured in large quantities at Syracuse, where the evaporating surface covers an area of over 12,000,000 square feet, and the season’s output amounts to about 3,500,000 bushels of salt, but between the solar and the vacuum processes the American salt-men have exploited the Pan and the Kettle processes of direct-fire evaporation, and the Steam Kettle and the Grainger processes of steam evaporation; all of which methods are employed to-day in the State of New York.

In the Pan process, several pans, having a width of 20 to 24 ft., a length of 100 ft. in two sections, and a depth of 12 in., are placed under one roof. Adjoining this front row of pans at the back are arranged a second row of pans, 20 to 24 ft. wide, 30 ft. long, and 12 in. deep, set from 12 to 16 in. higher than the front pans, to enable the easy transfer of brine by syphon from the back to the front pan. The grates are 3 to 4 ft. wide, by 5 to 6 ft. long, and the pan bottoms, which are directly over the fires are protected from a too intense heat by fire-brick arches, which decrease in width from the front to the back of the pan, while the air spaces between the arches increase in width in the same direction. Beyond 20 ft. from the front of the first section of the pan they cease altogether. To convey the heat as close to the pan bottom as possible, beyond the last arch, the flues are usually filled in with earth or plaster, and thus the distance between the pan and flue bottom is between 3 and 4 ft., or even less, at the end of the first pan, where a perpendicular wall, called a bridge wall, reduces the space to about 1½ to 2 ft., through which the products of combustion pass under the back pan and finally into a common chimney.

After the pans are properly cleansed they are white-washed with a thin milk of lime to prevent their rusting before they become thoroughly heated; the fires are started, and the pans are filled by syphons to a depth of about 6 in. with brine from the back pans. The former are so inserted that a constant flow of brine passes from the back pans into the last section of the front pans, and from these under the partition into the first section. Into the back pan flows a constant stream from the outside cistern, until the front pans are sufficiently full, when the flow is stopped. After a sufficient amount of salt has collected in the first section of the front pan it is removed to the “drip” for drainage. This is called drawing or raking the pans. The front pans are refilled from the back pan in which the brine has become considerably heated, and thus is prevented a too rapid cooling of the brine in the front pan, which would seriously interfere with the formation of a properly grained salt. For the same reason, the partition is placed in the front pan, since it prevents any cold brine from coming suddenly into the first section, but is compelled to enter at the bottom of the pan, where the temperature is at the highest.

For the purpose of aiding the formation of fine grained salt, butter, specially prepared soft soap, gelatine, or white glue are added, and when this variety of salt is made the pans are drawn every 45 to 60 minutes. In the manufacture of coarser grained salt, the drawing of the pans take place at intervals of from two to twelve hours, while the temperature is reduced from 229° F. to as low as 148° F., according to the size of the grain.

The Kettle process, which is exclusively employed on the Onondaga Salt Reservation, consists of from 60 to 100 hemispherical cast-iron kettles suspended or hung on “lugs” or pins in two parallel flues, called arches, ending in one chimney, which has a height of 50 to 100 ft., according to the length of the flues. In front the arches are provided with cast-iron, flat-topped grates, 3 ft. in width and 5 ft. long, perforated with holes ⅜ in. in diameter and 1 in. apart. These are well adapted for the burning of anthracite dust, which is now exclusively used for the purpose. The necessary artificial draught is furnished by a pressure blower. The kettles are from 23 to 26 in. in depth, and from 3 ft. 10 in. to 4 ft. 2 in. in diameter, with a capacity of 100 to 150 gallons. The distance from the bottom of the kettle to the top of the grate is 3 ft. 6 in., with a solid fire-brick arch in each, extending somewhat beyond the length of the grate. The distance from the bottom of the kettle to the crown of this arch is 10 to 12 in. Beyond the grate the fire-brick arches are constructed in sections, the air spaces between the arches increasing in size with the advancing distance from the grates. This construction allows the heated gases to pass through these spaces without striking the kettle bottoms directly. While the distance between the bottom of the front kettle and the top of the grate is 3 ft. 6 in., these flues decrease in depth as they advance towards the chimney, so that under the last kettle the distance is but 6 or 8 in. The kettles are hung as close as possible with their rims against each other, and the space between the walls and kettles above the lugs is properly covered by masonry, etc., for the purpose of confining all the heat as much as possible within the two arches.

The system of kettles is fed by means of a conduit connected with large wooden cisterns situated outside the building and sufficiently elevated to supply the brine contained therein by gravity to the kettles in the block.