M 102 -
MINERALS AND METALS.
The 296 samples of metals and minerals examined during the year comprised the following:-
1930 1929 1930 1929 Metals Minerals. Tin 109 174 Aluminium 4 ... Antimony 59 94 Antimony 5 ... Gold. ... 4 Molybdenite 1 ... Silver 13 ... Tin ... Τ ... Iron ... ... Graphite ¡ ... Wolfram... ... ... Other ores 13 ... Manganese 6 0 Total 82 119 Bismuth. 13 ... Total 118 178The adverse conditions prevailing in the commerce of the Colony during the year accounted for the decreased number of analyses of metals and minerals which the Laboratory was called upon to make.
WATER SUPPLIES.
The 240 samples of water were taken during the year at the various filter installations. Of these half were filtered and half were from unfiltered water. In addition to these, 1,244 samples were taken from taps in all parts of Hong Kong and Kowloon as a control on the water actually reaching the consumers. Samples from the filter beds were given a complete examination, whilst in the case of the tap samples, the free ammonia, free chlorine, the electrical conductivity and the hydrogen ion concentration were determined. Such an examination is designed to indicate merely whether any change has occurred since the water left the filter bed.
The great majority of samples of the raw unfiltered water in Hong Kong are acid, and give a hydrogen ion concentration value pH 6.5 to 6.8. Most of the filtered water is also slightly acid showing a value usually of pH=6.6—6.8.
As regards physical properties, colour and transparency, the water from the Paterson filtration plants at Bowen Road and Shing Mun was excellent, only one of the 24 samples taken showed colour in excess of six Lovibond colour units in a 24 inch stratum, whilst values of from 2 to 3 colour units were usual readings. In all these samples also, except one, the water had the maximum value for transparency, +100, in the case of the September sample from Bowen Road filter, the value fell to 90.