The efficiency ratio of chlorine to bleach has been reported upon by West.[4] From 1910-1913 the mixed filter effluents of the Torresdale plant at Philadelphia were treated with bleach but in November, 1913 the liquid chlorine process was substituted. On comparing the results obtained during the same months of the two periods it was found that, in general, 1 pound of liquid chlorine gave a slightly higher percentage purification than 6-7 pounds of bleach. Similar results were obtained at the other Philadelphia plants. The figures published by West show that the hypochlorite solutions used were abnormally strong (3.6-10.4 per cent of available chlorine), a condition that would increase the difficulty of extracting all the soluble hypochlorite. It was found indeed, that, under the most advantageous conditions, only 87 per cent of the available chlorine was extracted. The average chlorine content of the bleach used during 1912-1913 was 36.1 per cent but the figures given would indicate that at least 1.5 per cent, a reduction of 4.6 per cent of the total, was lost during storage. It would seem not improbable that the total loss under average conditions was not less than 20 per cent, which would reduce the efficiency ratio to 1:4.8-5.6. Hale[6] also made a comparison of the relative efficiency of liquid chlorine and hypochlorite of lime at New York, and the earlier results agreed with West's ratio of 1:6-7. An investigation showed that large quantities of chlorine were not extracted from the bleach and when this condition was rectified the total loss averaged only 4 per cent and the results obtained were equal to those given by the liquid chlorine machines. Hale's comparative figures are given in Table XXIII. TABLE XXIII.--COMPARISON OF LIQUID CHLORINE WITH EFFICIENT USE OF BLEACH--(HALE) ----------------+----------+-----------+------------+--------------- Treatment. | Water | Number of | Chlorine | Reduction | Treated. | Samples. | p.p.m. | of B. coli. ----------------+----------+-----------+------------+--------------- Bleach | Croton | 84 | 0.27-0.36 | 93% Liquid chlorine | Bronx | 84 | 0.27-0.36 | 93% ----------------+----------+-----------+------------+--------------- Hale concluded that, when efficiently used, the ratio of chlorine to bleach required to produce equal bacterial purification, approached 1:3.