Chap. 7.] Salt Works. 37 



taken up near Harwich. From other obfervations 

 alfo it has appeared, that water from near TenerirT 

 contained about one thirty-iecond of fait, and that fome 

 from Saint Jago contained fully one-fourth. Further 

 experiments are needed to afcertain the faltnefs of the 

 fea in different latitudes with precifion. 



The fait commonly ufed for culinary purpofes, and 

 known by the name of bay-falt, is obtained from the 

 water of the fea by evaporation. This evaporation is 

 in fome places performed by the heat of the fun, the 

 water being let into mallow trenches, in order to ex- 

 pofe as large a furface as poffible. This method is 

 pracYifed in the fourhern provinces of France, and on 

 a very large fcale near Aveiro in Portugal. In the 

 northern provinces, where the heat of the fun is not 

 fufficiently great, artificial fires are employed. In 

 fome fait- works thefe two methods are united ; and in 

 England, and countries where fait rock is plentiful, 

 that fubflance is diflblved in fait water, and then eva- 

 porated *. In very cold countries another method is 



employed 



* ' A great quantity of ro:k fait is ufcd at Northwich, in order 

 to ftrengthen their brine fprings, and a much greater quantity is 

 lent coafhvife to Liverpool, and other places, where it is ufed 

 either for ftrengthening brine fprings or fea- water ; much of this 

 rock fait was formerly exported to Holland, and it is itill fent 

 to Ireland for the fame purpofe. Rock fait, and the white fait 

 which is at Northwich, chiefly made from rock fait, is exported free 

 from the fait duty ; and I was informed, that the quantity, which 

 is annually exported from Northwich, is fo great, that if it paid 

 the duty, it would bring in to government, a fum not much fhort 

 of four hundred thoufands pounds a year. " According to the befl 

 accounts I have been able to procure, the grots duty on fait made 

 in South Britain, amounts annually to feven hundred thoufancj 

 pounds (a)." The duty on fait made at Northvvich is about 



feven ty 



(a) Camp. Sur. of Brit. Vol. II. p, 36, 



