Dr. A. Holmes — Non-German Sources of Potash. 345 



possesses a more valuable deposit which somewhat resembles Searle's 

 Lake; but here the salt crust is only 3 to 5 feet in thickness, 

 and the brine is not only less concentrated than in Searle's Lake but 

 contains less potash relatively to the other constituents. 



Tunis. — South of Gabes (long. 10° E.), in the lowland of the 

 Tunisian Shotts, a salt lake is worked for both bromine and potash. 

 A product known as " sebkainite ", which contains about 34 per cent 

 of potassium, is obtained by solar evaporation of the brine. Com- 

 mercial exploitation began in 1915, and the present rate of extraction 

 is equivalent to over 1,000 tons of KC1 per month. The plant now 

 being installed will gradually increase the production to four times 

 the present output, and will make possible the export of the 

 pure chloride, refined on the spot from crude salt such as is now 

 obtained. 



Saltpetre. 



Deposits of potassium nitrate are generally of organic origin, but in 

 Chile a small proportion is associated with the sodium nitrate deposits, 

 and in Brazil a deposit has recently been discovered containing 89 per 

 cent of KN0 3 . In the Eocene marls and limestones of Fergana in 

 Central Siberia saltpetre has been found to the extent of between 

 2 and 5 per cent over a very considerable area, and as fuel (coal and 

 petroleum) is abundant in the same district the conditions appear to 

 be favourable for its extraction. India, however, is the only large- 

 scale exporter of saltpetre, liehar being the chief district from which 

 it is obtained. The conditions of its formation are well described in 

 the Review of the Mineral Production of India, 1909-13, from which 

 the following paragraphs are extracted l : — 



" For the formation of saltpetre in a soil the necessary conditions are : 



(1) Supplies of nitrogenous organic matter ; 



(2) climatic conditions favourable to the growth and action of Winogradski's 



so-called nitroso and nitro bacteria, converting urea and ammonia 

 successively into nitrous and nitric acids ; 



(3) the presence of potash ; and 



(4) meteorological conditions suitable for the efflorescence of the potassium 



nitrate at the surface. 

 An ideal combination of these necessary circumstances has made the Behar 

 section of the Gangetic plain famous for its production of saltpetre. 



" In this part of India we have a population of over 500 per square mile, 

 mainly agricultural in occupation, and thus accompanied by a high proportion 

 of domestic animals, supplying an abundance of organic nitrogen. . . . 



"With a population largely using wood and cow-dung for fuel, the soil 

 around villages naturally would be well stocked with potash, and, finally, with 

 a period of continuous surface desiccation, following a small rainfall, the sub- 

 soil water, brought to the surface by capillary action in the soil, leaves an 

 efflorescence of salts, in which, not surprisingly, potassium nitrate is con- 

 spicuous. Under these conditions Behar has for many years yielded some 

 20,000 tons of saltpetre a year." 



Kelp. 



Since the beginning of the eighteenth century seaweed has been 

 utilized along various parts of the Scottish and Irish coasts as a 

 source of potash and iodine, but owing to foreign competition the 



1 Sir T. H. Holland & L. L. Fermor, Bee. Geol. Surv. India, vol. xlvi, 

 pp. 210-15, 1915. 



