M(1)46
WATER SUPPLIES.
The examination of the Colony's water supplies is a part of the work of the Laboratory which has rapidly increased in the past few years. The following Table shows the number of samples examined during each of the past seven years:----
Year. 1921. 1922. 1923. 1924. 1925. 1926. 1927. Samples. 36 56 164 286 595 903 1248The 1248 samples examined during 1927 comprise the regular samples taken of the filtered and unfiltered water at the various filtration plants and also a large number of tap samples from houses and office buildings all over the City and Kowloon to test the condition of the water as it reaches the consumer.
A considerable amount of work was done in connection with the new Bowen Road mechanical filtration plant, samples of local lime being examined for percentage of free lime, also samples of alumina-ferric used in the purification of the water, for strength. Many determinations of the colour of the filtered water were made with the Lovibond tintometer to check the efficiency of the beds and to regulate the dose of coagulants added.
The hydrogen-ion concentration of the filtered water is now being determined daily in order to keep the water within the correct limits of alkalinity.
The water from the various filter beds has been found to be satisfactory on the whole, as regards colour, transparency and chemical purity. Most of the City supplies showed a colour of well under 10 Lovibond colour units, the highest reading being from the Elliot beds in August (18.9 units); this was however quite exceptional. No nitrites or heavy metals nor excess free chlorine were found, the albumenoid ammonia in no supply reached 0.005 parts per 100,000 and was usually below 0.003. The oxygen absorbed was in nearly all cases below 0.050 per 100,000 which is very satisfactory.
SPECIAL REPORTS.
Special Reports have been prepared during the year on: "The preparation of Vitamine B Extract for Beri-beri treatment", "The composition of certain Chinese ores", "The specification for Pure Rapeseed Oil".