Modern Gasworks Practice

588 MODERN GASWORKS PRACTICE is completed all the daily samples are to be at once mixed and broken down, and for this purpose coning and quartering is the best method. The well-mixed oxide is poured several times on to a given centre ; this ensures an even distribution of both lumps and fines in the form of a cone. The cone is then flattened and quartered. Two opposite quarters are discarded and the remainder again mixed, coned and quartered until the quantity is reduced to a convenient amount. This is now crushed until it will all pass through a J-inch mesh sieve, and at once bottled. The above operation must be carried out as quickly as possible to avoid alteration in the moisture content of the sample. Samples should be of at least 1lb., and must be packed in air-tight bottles or tins ; no other receptacle may be usecl In taking the necessary samples one must always be sealed and retained for reference. Testing—Before carrying out tlie analysis, the whole of the sample is further inti-mately mixed and broken down and reduced to about 100 grammes, which is ground so that the whole quantity passes through a 20-mesh sieve. Analysis Moisture—Five grammes are dried for three hours at 100° C. in a water oven. The loss of weight found on cooling and reweigliing represents the moisture. Sulphur and Tar—The dried residue from the moisture determination is to be ex-tracted for two hours in a Soxhlet’s apparatus with. freshly distilled carbon bisulphide. The carbon bisulphide is then distilled off, the flask cautiously blown out with air and dried for two hours at 100° C. in the water oven. The flask is then placed on a hot sand bath until the sulphur has just fused, care being taten that no loss by over-heating and volatilization takes place. After the flask has cooled completely it is again carefully blown out with dry air and again weighed. The increase in weight multiplied by 20 gives the percentage of sulphur plus extracted tarry matter. Estimation of the Sulphur—15 c.c. of concentrated (95 per cent.) sulphuric acid are poured on to the sulphur and tar in tlie flask, and the whole is heated for two hours at 100° C. in a water oven. After cooling, the contents of the flask are diluted with water, filtered, washed free from acid and dried. The dried Alter paper with contents is placed in a Soxhlet’s tube and again extracted with carbon bisulphide. The bisulphide is distilled off, and the residue fused exactly as described above. The weight of the residue in the flask multiplied by 20 gives the percentage of sulphur free from tarry matter in the oxide originally taken. THE OPERATION OF DRY PURIFIERS Present-day systems of purification may be classified under two headings, namely-— («) Series purification. (b) Rotation purification. „ (1) Forward system. „ (2) Backward system.