VOL. XVIII. (i) EXCURSION— DROITWICH AND STOKE WORKS 21 



The salt is obtained in the form of brine and occurs in the Upper Keuper 

 Marls. The Upper Keuper Marls are of a prevalent red colour and have a 

 very considerable ,s;eo<?raphical extent in the English Midlands. It is thought 

 that the conditions which obtained in England at the time that these 

 deposits were formed, were very similar to those which now obtain in the 

 salt-lake district of Utah. Water which has percolated the red rocks and 

 become saturated with salt constitutes the practically inexhaustible supply 

 of brine drawn upon bv the Works. The brine has an almost constant 

 specific gravity of i'2i2g at I5°C, and contains about 2 1 , 500 grains of salt 

 (Na CI.) to the gallon, togetlier with small quantities of other salts of lime 

 and magnesia. The brine is delivered to a large reservoir, from which it is 

 drawn off to evaporating pans as required, and is of sufficient purity to 

 allow of the manufacture of salt for all purposes, including domestic and 

 table use, made by the simple process of evaporation, no refining or re-crys- 

 tallization being required. 



The process of manufacture is extremely simple. Shallow rectangular 

 tanks of wrought iron are erected, having a capacity varying from a few tons 

 up to 1 50 tons of salt per week, the largest being 50 or 60 feet long, and 

 nearly 20 feet wide. These tanks, or evaporating pans, are fixed over coal 

 furnaces, having a system of flues extending under their whole area. Others 

 are heated by steam, while a few circular closed pans are in use, having 

 shallow open pans attached to them for crystallizing and collecting the 

 manufactured salt. 



Various grades of salt are produced of different degrees of fineness, the 

 size of crystals being regulated largely by the rapidity of evaporation. Thus, 

 the finest table salt is produced at the highest degree of evaporation. 



The ordinary bar salt is made in open pans heated by coal fires. As the 

 salt crystallizes it is lifted from the mother liquid and placed in wooden 

 moulds to drain. These moulds are then carried to drying rooms, and when 

 the salt has become sufficiently firm it is withdrawn from the mould, and 

 when quite dry is ready for the market. 



Coarser qualities, that is, grades with larger crystals, are made by 

 evaporating very slowly at a low temperature, some of the pans being left 

 for a month before being " drawn." 



For various purposes the salt is ground between iron rollers and packed 

 as a fine powder, while some of the large blocks are cut by means of circular 

 saws for sale as penny and halfpenny bars. 



The output of the works is said to be 150,000 tons per annum. The 

 finished product is almost pure chloride of sodium, containing mere traces of 

 the sulphates of lime, soda and magnesia. 



Analysis of Sample of Worcestershire Dairy Salt. 



Sodium Chloride (Salt) . . 98-29 



Calcium Sulphate . . . . '87 



Magnesium Sulphate . . . . '06 



Sodium Sulphate . . . . '74 



Moisture . . . . . . "04 



The Members left Stoke Prior Station at 4.10 p.m. [L.R.] 



