TfeL. XII.] PHILOSOPHICAL TRANSACTIONS. 46l 



than when the weather is temperate. In frosty weather the cold strikes the 

 akim too soon, not giving time for the nitre and slam to sink to the bottom, 

 and thus they are mixed with the alum. This produces double the quantity; 

 but being foul it is consumed in the washing. 



When the liquor has stood 4 days in the cooler : then that called mothers is 

 scooped into a cistern, the alum remaining on the sides and at the bottom ; and 

 from thence the mothers are pumped back into the boiler again. So that every 

 5 days the liquor is boiled again till it evaporate, or turn into alum and slam. — 

 The alum taken from the sides and bottom of the cooler is put into a cistern, 

 and washed with water that has been used for the same purpose, being about 12 

 pounds weight. After which it is roached in the following manner : — Being 

 washed, it is put into another pan with a quantity of water, where it melts and 

 boils a little ; it is then scooped into a large cask, where it commonly stands 

 10 days, and is then fit to take down for the market. The liquors are weighed 

 by troy-weight. So that half a pint of liquor must weigh more than so much 

 water, by so many penny weights. 



The English Green Copperas. By Dan. Colwall, Esq. N° 142, p. 1056. 



Copperas-stones,* which some call gold-stones, are found on the sea-shore in 

 Essex, Hampshire, and so westward. There are great quantities on the cliffs ; 

 but not so good as those on the shore, where the tides ebb and flow over them. 

 The best of them are of a bright shining silver colour : the next such as are of 

 a rusty deep yellow : the worst, such as have gravel and dirt in them, of a dull 

 or umber colour. In the midst of these stones, are sometimes found the shells 

 of cockles, and other small shell fishes ; also small pieces of the planks of ships 

 and of seacoal. The brightest of these stones are used for wheel-lock pistols 

 and fusees. — ^To make the copperas, they prepare beds according as the ground 

 will permit. Those at Deptford are about 100 feet long, 15 feet broad at the 

 top, and 12 feet deep, shelving all the way to the bottom. They ram the bed 

 very well first with strong clay, and then with the rubbish of chalk ; whereby the 

 liquor which drains out of the solution of the stones, is conveyed into a wooden 

 shallow trough, laid in the middle of the bed, and covered with a board; being 

 also boarded on all sides, and laid lower at one end than the other, the liquor is 

 conveyed into a cistern under the boiling-house. — ^When the beds are indiffer- 

 ently well dried, they lay on the stones about 2 feet thick. — These stones will 

 be 5 or 6 years before they yield any considerable quantity of liquor; and before 

 that, the liquor they yield is but weak. They ripen by the sun and rain : yet 



• Martial pyrites j from which by the process here described is extracted sulphate of iron, or 

 green vitriol. 



