Four cubic inches of brine were evaporated to dryness very slowly, in a heat which was not suffered to rise above 212°, and towards the close of the evaporation it was kept between 170° and 180°. The residuum was reduced to powder, and again kept for an hour in a heat of about 180°. The different brines yielded the following quantities of entire salt.
|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.
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.