_Penot's Method._ Dilute the hypochlorite solution with 15 c.cms. of water and titrate with a solution of N/10 sodium arsenite using starch-iodide paper as an external indicator. Each c.cm. of solution used = 1.755 per cent of available chlorine (1 c.cm. = 0.00355 grm. available chlorine). The use of an external indicator makes this process a slow one and to overcome this objection Mohr proposed the addition of an excess of sodium arsenite solution and then titrating with N/10 iodine solution after adding a few drops of starch solution. Griffen and Hedallen[2] compared these three methods and found that Penot's method and Mohr's modification of that method gave results which were 0.6 per cent lower than those obtained by Bunsen's method. For a separate estimation of the chlorine present as chloride, chlorate, and hypochlorite the method given in Sutton's Volumetric Analysis, 10th edition, page 178, should be followed. _Storage Liquor._ This is tested by any of the above methods. It has been proposed to determine the strength of the bleach solution by the use of a hydrometer but the results are not sufficiently accurate and the method cannot be recommended. If bleach is properly broken up and thoroughly agitated in the mixing tank at least 95 per cent of the available chlorine should be extracted. The efficiency of the extraction process is checked by comparing the tests of the storage liquor with those of the dry bleach and each batch of liquor should be tested daily. It is sometimes advisable to take two samples from each tank, one soon after a tank has been put into operation, and a second sample at the end of the run. Considerable differences are occasionally found between these samples and are due, either to inadequate agitation of the liquor in the storage tank, or inefficient mixing in the mixing tank. If the results are irregular the former is the more probable cause but if the second sample is invariably stronger the mixing tank operations should be investigated. The increased concentration of the second sample is due to unextracted bleach passing out of the mixing tank and gradually becoming leached as the tank contents are run off. If the bleach is lumpy and is not subsequently broken up, losses are almost inevitable. Hale[3] found that during the period when the New York City supply was being treated with bleach it was necessary to constantly check the operations of the labourers by frequent samples. "During one week about 95 per cent of the chlorine added was actually applied, the second week it dropped to 85 per cent. and the third week to 75 per cent. Whenever a poor run is called to the attention of the labourers, results improve."