▼OL. XII.] PHILOSOPHICAL TRANSACTIONS. 45^ 



In calcining these stones, the wind often does hurt, by forcing the fire in 

 some places too quickly through the mineral, leaving it black and half burned; 

 and in others burning it too much, leaving it red. But where the fire passes 

 slowly, and of its own accord, it leaves the mineral white, which yields the best 

 and greatest quantity of liquor. 



The mineral thus calcined, is put into pits of water, supported with frames of 

 wood, and rammed on all sides with clay, about 10 yards long, 5 yards broad, 

 and 5 feet deep; set with a current, that turns the liquor into a receptacle, 

 from whence it is pumped into another pit of mineral. And thus every pit of 

 liquor before it comes to boiling, is pumped into four several pits of mineral ; 

 and every pit of mineral is steeped in four several liquors, before it be thrown 

 away; the last pit being always fresh mineral. The mineral thus steeped in 

 each of the several liquors about 24 hours, is of course four days in passing tlie 

 four several pits, from whence the liquors pass to the boiling-house. 



The water, or virgin-liquor, often gains in the first pit 2 pounds weight ; in 

 the second it increases to 5 pounds weight ; in the third to 8 pounds weight ; 

 and in the last pit, which is always fresh mineral, to 12 pounds weight; and so 

 in this proportion, according to the goodness of the mineral, and the proper 

 calcining : for sometimes the liquors passing the four several pits, will not be 

 above 6 or 7 pounds weight. Yet often the liquor of 7 or 8 pounds weight 

 produces more alum than that of 10 or 12 pounds, either from the badness of 

 the mineral, or, as usually, the bad calcining of it. And if, by passing the weak 

 liquor through another pit of fresh mineral, you bring it to 10 or 12 pounds 

 weight, yet there will be less alum with it, than when it was but 8 pounds 

 weight. For what it gains from the last pit of mineral, will be mostly nitre and 

 slam, which spoil the good liquors, and disorder the whole house, until the 

 slam be wrought out. What they call slam is first perceived by the redness of 

 the liquor when it comes from the pit, occasioned either by the badness of the 

 mineral, or more commonly the over or under calcining it ; which in the settler 

 sinks to the bottom, and there becomes of a muddy consistence and a dark 

 colour. That liquor which comes whitest from the pits is the best. When a 

 work is first begun, they make alum of the liquor only that comes from the pits 

 of mineral, without any other ingredients. And so it might continue, but that 

 it would spend so much liquor as not to quit cost. 



Kelp is made of a sea-weed, called tangle. It grows on rocks by the sea side, 

 between high and low water mark. Being dried it will burn and run like pitch; 

 when cold and hard it is beaten to ashes, steeped in water, and the lees drawn 

 off to about 2 pounds weight. 



Because the country people who furnish the work with urine, sometimes mix 



3 N 2 



