320 LECTURES TO SCIENCE TEACHERS. 



at Liverpool one cubic metre of chamber uses 5*25 kilos 

 of sulphur per week, and at a second works of the same 

 firm at Widnes, 6-3 kilos are used for the same space, and 

 a production of 290 parts of strong acid for every 100 of 

 sulphur burnt is their average. On the Tyne the numbers 

 are similar, and at the Washington Works, on the Wear, 

 the average of ten years' work shows that 100 parts of 

 sulphur yielded 292 parts of strong acid, whilst the average 

 quantity of nitrate of soda needed is 5*5 for every 100 

 of sulphur received. 



In the Rheinau Works, near Mannheim, in Germany, one 

 cubic metre chamber space takes 3 '8 8 kilos of sulphur per 

 week, giving 11*40 kilos of H 2 S0 4 , so that 100 of sulphur 

 yield 294 of strong acid, and 6*5 parts by weight of nitrate 

 of soda and 210 parts by weight of steam, are needed to 

 complete the decomposition. 



In order to convert 100 parts of sulphur into sulphuric 

 acid, about 210 parts of water in the form of steam are 

 needed. This steam is costly in its production, and 

 Dr. Sprengel has recently proposed to reduce this item of 

 expenditure by employing a jet of water in the form of 

 spray, or in a state of very minute division. 



None of these processes, you will see, yield us chemically 

 pure acid. For this purpose the acid must be distilled to 

 get rid of the arsenic, lead, and other non-volatile matter 

 which the rectified acid contains. Even then the acid is not 

 perfectly pure, as it contains water. This cannot be got rid of 

 by distillation, but if we cool the distilled liquid, the pure acid, 

 containing 100 per cent, of H 2 S0 4 , can be crystallised out. 



In some works, both here and on the Continent, sulphuric 

 acid made from pyrites is freed from the arsenic contained 

 in it by being brought into contact with sulphuretted 

 hydrogen. The arsenic is separated as the trisulphide 

 which settles out from the acid. To effect this the sul- 

 phuric acid, before concentration, is made to flow in divided 

 streams down a tower of lead five feet square and fifteen 

 feet high, the fall of the acid being retarded by a large 

 number of bars of wood covered with lead, which stretch 

 horizontally across the tower. A current of sulphuretted 

 hydrogen gas, generated, as in the laboratory, by the action 

 of sulphuric acid on ferrous sulphide, passes up the tower, 

 and thus meets the acid in its descent. 



