The results obtained by the author in Ottawa are similar to those of Hale. During the earlier period of the bleach treatment a dosage of 1.5 p.p.m. of available chlorine was required to obtain satisfactory purification but various improvements that were subsequently made enabled the quantity to be reduced to 0.8 p.p.m. The same raw water usually requires 0.75 to 0.80 p.p.m. of liquid chlorine to obtain the same purification. The total losses in the Ottawa bleach plant averaged 6-8 per cent and based on these figures the efficiency ratio is approximately 1:3.5. Ratios as low as 1:3.5 can only be obtained by the supervision of a chemist and this analytical control involves additional expense that must be charged against the bleach process. No chemical analyses are necessary for the control of liquid chlorine plants. _Disadvantages of Liquid Chlorine Plants._ The main objection to the use of liquid chlorine is that the slight leaks of gas occur occasionally and unless removed by forced ventilation may produce a concentration of chlorine that will injure the operators. Pettenkofer and Lehmann[7] found that 0.001-0.005 per cent of chlorine in air affected the respiratory organs; 0.04-0.06 per cent produced dangerous symptoms, whilst concentrations exceeding 0.06 per cent rapidly proved fatal. The danger of gas leakages can be eliminated by placing the apparatus in a small separate room provided with a fan and a ventilation duct. By the liberal use of glass in the construction of the room, the operation of the plant can be seen at all times without entering the chamber. A portion of the liquid chlorine apparatus is made of glass and is consequently easily fractured. Duplicates of the glass parts should be kept in stock to prevent interrupting the supply of gas; a duplicate machine is also advisable in large installations. _Cost of Treatment._ Prior to the outbreak of war in 1914, liquid chlorine sold at 10-11 cents per pound in small quantities and for 8-9 cents per pound in large shipments. In 1917 the price was 18-20 cents per pound for small quantities and 15 cents upwards for large contracts. Canadian prices are 25 per cent higher. The amount of chlorine required for satisfactory disinfection (see Chapter III) depends upon the nature of the water and the cost of treatment varies accordingly. In the majority of plants the cost varies from 25-90 cents per million gallons. _Popularity of Process._ Since 1913, when the first commercial liquid chlorine machines were used, the popularity of this process has increased in a most remarkable manner. In 1913 over 1,700 million gallons per day were treated with hypochlorite; in 1915, 1,000 million gallons per day were treated with liquid chlorine and an approximately equal amount with hypochlorite; in January 1918, the amounts were 3,500 million gallons per day (liquid chlorine) and 500 million gallons per day (hypochlorite).