Saturday, May 21, 2016

The History of Saltpeter - XIV

In our last post, we studied how saltpeter was produced in the eastern regions of India, namely Bihar and Bengal. In today's post, we will study how it was produced in some of the other drier regions in India in the northern, central and southern parts.

Saltpeter Crystals. Click on the image to enlarge. Public domain image.

In our last post, we noted that the saltpeter production in the eastern regions of India was mainly done by a caste/tribe of people called nuniahs or luniahs, who specialized in this type of work. In the other regions of India, saltpeter production was done on a part-time basis by farmers, potters etc. These people would sell the high quality saltpeter crystals to others and keep some of the nitrated earth for themselves, to use as fertilizer for their fields. 

The following description is taken from The Agricultural Ledger, Volume 12, published in 1905, by the Office of the British Government in India, based on a report by David Hooper. The author based his description on a personal study of the saltpeter industry at Hansi, in the Hissar district of northern India, during the hot summer of 1902.

In this district, the nitrated soil is collected at Hansi fort (also known as the Asigarh fort, because of a historic sword manufacturing factory within its walls), an ancient ruin existing since about 700 AD or so, and rebuilt in the 12th century.

Views of the ruins of Asigarh fort at Hansi, India from different angles. Click on the image to enlarge.
Image licensed under the Creative Commons Attribution-Share Alike 4.0 International License by Amrahsnihcas 

A painting of Asigarh Fort and its surroundings at Hansi by Sitaram in 1815

The soil around the walls and moat of this old ruin contains nitrates and a sum of 300 per annum is paid to the Government for the privilege of collecting it. The earth is transported by donkeys, to the factory situated by the side of a main road outside of town. The arrangement of the beds for leaching the nitrous earth and evaporating the nitre liquor is shown in the following sketch:

A = Beds or filters (kurias) for the filtration of the nitrous earth.
B = Beds (patas or kiaris) for evaporating the nitre liquid.
C = Channels to conduct the liquid to the evaporating beds.
R = Jhela or reservoir.
P = Pit for storing the saltpeter
W = Well for supplying water.

The kurias (or filters, we encountered this word in our previous post) are 25 to 30 feet (7.6 - 9.1 meters) in length, 6 feet (1.8 meters) in width and 1 foot (0.3 meters) in depth. There are two of the kurias, which are sometimes sub-divided and arranged in two rows, running parallel, and situated on a broad hillock raised 3 to 4 feet (0.9 - 1.2 meters) above the ground. The beds are made of plastered clay or lime and are practically water-tight. The two evaporating beds are built on the level ground, and have concrete floors and sides. These are about 6 inches (0.15 meters) deep  and 25 to 40 feet (7.6 - 12.2 meters) square. They communicate with one another, and the smaller bed, which is raised slightly above the larger ones and is nearer the mound, serves as a reservoir for collecting any nitre water that is not required by the other beds.

The nitrated earth is carried to the kurias and is packed in them to a depth of 8 inches (0.2 meters). It is sometimes mixed with ashes in order that the soil may remain open and porous when the water is added, and possibly also with the object of decomposing the calcium and magnesium nitrate with the carbonated alkali. When the packing of the earth is complete, the water from the well (W in the figure above) is baled up by earthen pots and poured over the nitrous soil and is allowed to filter slowly through it in order to dissolve the saline matter. The saturated liquor flows off in a small stream, through the concrete channel, into the large shallow evaporating beds. Meantime, the other bed is filled as described with earth and water, and filtration and drainage go on regularly in rotation in the filters until enough liquid is obtained to fill the lower evaporating beds. The exhausted earth is removed from the kurias when the water extract has been fully drained off.

As the weather in this part of India is dry and hot during the summer, the liquid is allowed to evaporate in the shallow beds (B in the figure above), due to the heat from the sun. As the yellowish liquid in the evaporating beds becomes more concentrated, the nitre begins to crystallize at the sides and bottom, and after about seven days, most of the nitre has solidified and it is raked together into parallel ridges along the length of the bed about 3 feet (0.9 meters) apart. The mounds of crude crystals, after further drying, are collected together into heaps and then carried in baskets to a pit made in the ground a short distance away. The evaporating kurias are never allowed to become quite dry during the working season, in order to avoid cracking; as soon as the damp crystals are removed to the pits, fresh nitre liquid is run in from the reservoir, and evaporation is continued. Each kuria is said to yield 20 to 30 maunds (1645 - 2470 lbs. or 745 - 1120 kg.) of crude saltpeter per week. The nitre prepared in this manner is placed in the storage pit until it is sold. 

This method of preparing saltpeter using the heat of the sun, was practiced in the drier parts of India, where the climate permitted it. However, the crude saltpeter obtained by this method was not considered to be of as good quality as the crude saltpeter produced by artificial heat (which we studied in the previous post).

The crude saltpeter produced was then refined in a larger factory. We will study the process of this in the next couple of posts.

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