THE PRODUCTION OF SULPHURETTED HYDROGEN 27 



The sand consists of clay, fine particles of silica, and organic 

 debris, interspersed with black particles which in most cases 

 form a covering to the particles of silica. 



(3) The Rocks in the Clyde Drainage Area. — To the North 

 are the Campsie and Kilpatrick Hills, which consist almost 

 entirely of basaltic lavas rich in magnetite, with an iron con- 

 tent amounting to lO — 15 per cent, or more. On the South 

 the drainage area includes the hills that extend through 

 Renfrewshire and Lanarkshire, which are basaltic lavas. 

 Along the course of the River Clyde the rocks are mostly 

 Carboniferous, and include the Carboniferous Limestone 

 Series containing coal and ironstones, and the Coal Measures 

 in which these are also abundant. These ironstones contain 

 FeCOg, but the carboniferous coal and shale beds also contain 

 large quantities of FeS. Finally, in the upper reaches of the 

 Clyde, and also on the lower reaches on the north side we 

 find the Old Red Sandstone Series, the rocks of which are 

 composed of a sandstone with an iron oxide matrix. It is 

 therefore natural to find a fair quantity of iron in the com- 

 position of the sands on the shore of the Clyde. 



(4) Formation of Ferrous Sulphide (FeS). — The statements 

 detailed above show that the conditions are favourable for 

 the formation of ferrous sulphide. The amount of organic 

 matter is large enough to provide ample food for the nourish- 

 ment of saprophytes ; there is ample moisture to permit of 

 their development ; those organisms are present in abundance 

 which are capable of bringing about the production of hydrogen 

 sulphide ; and in addition the sand is rich in iron. It was not 

 found possible by a simple chemical analysis to make a direct 

 quantitative estimation of the amount of ferrous sulphide in 

 the sand. From work done in the author's laboratory it was 

 concluded that the black colour was entirely due to ferrous 

 sulphide, because when the iron was extracted, and the residue, 

 suspended in water, treated with sulphuretted hydrogen, 

 no black colour was produced. On the other hand, a sample 

 from which the iron had not been extracted but which had 

 lost its black colour by drying regained its colour when 

 sulphuretted hydrogen was passed over it. 



