VOL. XLT.] PHILOSOPHICAL TRANSACTIOKS. 581 



known, Lundmarck tells us, potash is sold for little more than a farthing a 

 pound, which costs our workmen near 6 pence. 



But this is not the only inconvenience we labour under for want of this com- 

 modity ; the salts we are chiefly supplied with, are perhaps the worst of any, and 

 unfit for many purposes for which potash is used. The only potash almost to 

 be met with here, comes from Russia, Sweden, and Dantzic, or is made in 

 England. These are all made either of wood or fern-ashes, whose salts are never 

 so pure and white at the best, as some others : but by the way of making them, 

 and the experiments on them above mentioned, they appear to be impregnated 

 with coal, smoke, and soot, which renders them still more foul and impure, 

 makes them of a black, brown, or green colour, and of a peculiar sulphureous 

 quality. On this account they are entirely unfit for making white glass : they 

 make a very coarse and strong kind of soap ; they are too foul, sharp, and cor- 

 rosive for bleaching, and are as unfit for dyeing, at least many colours. 



It is perhaps for this reason, that the workmen here make all their white glass 

 with salt-petre ; which must not only be more costly, but Neri, Merrett, and 

 others tell us it is not so good, at least for the better sorts of glass, as a sharper 

 lixivial salt. What they use for dyeing he is not so well apprised of: it is said, 

 they use the volatile alkali of urine ; but the French potash, made of the lees of 

 wine, is generally allowed to be the best for that purpose. So likewise the Ali- 

 cant potash is reckoned much the best for bleaching, and making soap; as 

 the Syrian and Egyptian is for making glass. 



These purer kinds of potash are all made of herbs, that grow only in the 

 more southern climates, whose salts are finer and whiter, and less acrid and cor- 

 rosive than the salts of wood, or most other vegetables ; and by the way of ex- ' 

 tracting them by calcination in a more open fire, they are more free of coal, 

 smoke and soot, or any other heterogeneous mixture. On this account they are 

 much better for the purposes above mentioned, than the coarse and foul kinds 

 of potash that our people are supplied with. 



AH we have of these kinds of potash, it seems, comes only from Spain ; for 

 which reason our people were obliged to petition to allow the importation of pot- 

 ash from thence, during the late war ; as appears by an order of the king and 

 council of the 24th of June 1742 ; since they could not do without it in many 

 manufactures : so that it may be worth our inquiry, to know what it is that 

 produces so necessary a commodity. 



This kind of potash is commonly called barrilha, from a herb of the same 

 name in Spain that produces it. The first account we have of this barrilha is 

 from Amatus Lusitanus, who leaves us much in the dark about it. It is gene- 

 rally said in England to be a plant pretty well known to the botanists by the 

 name of ficoides Neapolitana, flore candido. Hort, Lugd. Bat. ; but for what 



