Modern Gasworks Practice

568 MODERN GASWORKS PRACTICE SO 2, and then a weak solution of pure sulphate of copper in slight excess, the whole heated a short time on the water-bath, filtered. hot, and washed. The filter containing the cuprous sulphocyanide is transferred to a beaker (pre-ferably the one in which. the precipitation took place, as small portions of the pre-cipitate may be adhering to the glass). From 25 to 50 c.c. of normal caustic soda free from Chlorides are added, and about 100 c.c. of boiling water, and the whole heated on the water-bath., with frequent stirring, until the cuprous oxide becomes sufficiently granulär to filter. Filter while still hot, wash well with hot water, and allow the combined filtrate and washings to cool. Acidify slightly with pure dilute nitric acid, add a few drops of ferric sulphate solution, and titrate with decinormal silver nitrate until the colour disappears. Towards the end of the titration add a few more drops of ferric sulphate to increase the distinctness of the end reaction. Example.—23'5 cubic feet of gas were passed through the wash-bottles in twenty-four horns, and the contents were made up to 1,000 c.c., of which 50 c.c. (representing 1-175 cubic feet of gas) were taken. After proceeding as above, 32-7 c.c. of deci-normal silver nitrate were required for titration— 1 c.c. of silver nitrate = 0-0076 gramme of ammonium sulphocyanide. 32-7 „ „ =0-2485 i.e. 1’175 cubic feet of gas contain 0-2485 gramme of ammonium sulphocyanide, or 100 cubic feet of gas contain 21-1 grammes of ammonium sulphocyanide. There are 15-43 grains in 1 gramme, therefore 21-1 X 15-43= 325-5 grains of ammonium sulphocyanide per 100 cubic feet. The molecular weight of ammonium sulphocyanide is 76, and that of hydrocyanic 27 acid 27, so that 325-5 X — = 115-6 grains HCN per 100 cubic feet. The above test is usually made use of only when sulphocyanide processes are in operation. When ferrocyanide plants are employed the following method. is preferable:— A 30 per cent, solution of caustic soda or caustic potasli is mixed with. a 12 per cent, solution of ferrous sulphate in the proportion of 5 to 1. The mixture is poured into three Woulffe’s bottles, and gas is passed through at the rate of 1 cubic foot per hour. After about 10 cubic feet of gas have been passed the mixture (col-lected from the three Woulffe’s bottles) is washed into a graduated flask, and a portion is taken for analysis. The mixture is boiled until free from ammonia, and is then filtered. The filter paper is washed with hot water until a few c.c. on being acidified with hydrochloric acid give no blue colouration on the addition of ferric chloride. The filtrate and washings are acidified with hydrochloric acid and the cyanogen is precipitated with. ferric chloride, as Prussian blue. The whole is then poured into a tared filter paper and well washed with hot water until the filtrate is free from iron salts. The filter paper and contents are then. dried and weighed. Example.—10 cubic feet of gas were passed through the caustic soda and ferrous sulphate mixture. The mixture washings were then made up to 500 c.c., of which