VOL. XII.] PHILOSOPHICAL TRANSACTIONS, 4^3 



nace. Then, instead of pumping cold liquor into the boiler to supply the waste 

 in boiling, which checked the work sometimes 10 hours, Sir Nicolas has a vessel 

 of lead, which he calls a heater, placed at the end of the boiler, and a little 

 higher, supported by bars of iron as before, and filled with liquor, which by a 

 conveyance of heat from the furnace is kept near boiling hot ; and hence he 

 continually supplies the waste of the boiler, without hindering the boiling. 

 Thirdly, by putting in due proportions of iron from time to time into the boiler. 

 As soon as they perceive the liquor to boil slowly, they put in more iron, which 

 will soon quicken it. If they do not continually supply the boiling liquor with 

 iron, the copperas will gather to the bottom of the boiler and melt. And so it 

 will do if the liquor be not presently drawn off from the boiler into a cooler, so 

 soon as it is sufficiently done. 



The cooler, made of tarras, is oblong, 20 feet long, g feet over at the top, 

 and 5 feet deep, tapered towards the bottom. Into this they let the liquor run, 

 as soon as it is boiled enough. The copperas herein will be gathering or shoot- 

 ing 14 or 15 days; and it gathers as much on the sides as in the bottom, viz. 

 above 5 inches thick. Some put bushes into the cooler, about which the copperas 

 will gather. But at Deptford they make no use of them. That which sticks 

 to the sides and to the bushes is of a bright green ; that in the bottom of a foul 

 and dirty colour. — At the end of 14 days, they convey the liquor into another 

 cooler, and reserve it to be boiled again with new liquor. — ^The copperas they 

 shovel on a floor adjoining, so that the liquor may drain from it into a cooler. 

 The steam which comes from the boiling is of an acrimonious smell. 



Copperas may be boiled without iron, but with difficulty.* Without it the 

 boiler will be in danger of melting. Sometimes in stirring the earth on the 

 beds^ they find pieces of copperas produced by lying in the sun. 



Account of the Salt Springs and Salt making at Droitwich in JVorcestershire. By 

 Dr. Thomas Rastell. N° 142, p. 1050. 



The country has no great hills, but many small risings. On the other side 

 the river Severn are Aberly Hills, at about 7 miles distance from us. There are 

 many salt springs about the town, which is seated by a brook-side called Sal- 

 wark-Brook, which arise both in the brook and in the ground near it, though 

 there are but 3 pits that are made use of. The plants growing about the springs 

 I find much the same as in other places ; but where the springs are saltest there 

 grows nothing at all; only by the brackish ditches there grows aster atticus, 

 with a pale flower, which I find no where else with us. 



* The unsaturated vitriolic acid acts upon the iron thus added, and consequently the quantity of 

 ▼itriolic salt (green copperas) is increased. 



