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passion-fruit, orange, and pasture plants were examined with the object of detecting any relations between plant diseases and the quantities of trace elements present. Attention was drawn to the possibility of molybdenum deficiency. There was some indication that nickel might be significant. An electrographic method for the quick identification of the metals of electrical contact points was devised for the Post and Telegraph Department. The X-ray diffraction apparatus was found useful for the identification of (jrystalline components of pigments, boiler scales, and the corrosion products of metals. It was also used in an attempt to correlate the structure of different samples of plaster-of-paris with the lasting properties of the plaster moulds used for ceramic articles. Information and advice were given on various electroplating problems and an investigation was made of the rapid pitting of pure lead by chromic-acid plating solutions. Information circulars were prepared on the plating of plastics and on porous chromium plating. METALS AND CORROSION Analyses were made of metals and alloys for Government Departments and for manufacturing firms. Assistance was given to the physical and engineering branches of the Department on the chemical and metallurgical aspects of industrial problems. Many problems were investigated directly for industry. A method of cleaning type matrices was developed for a firm that was having trouble through fouling of matrices by molten type metal. The corrosion of a launch engine manifold was concluded to be due to the action of sulphate-reducing bacteria derived from a sewage effluent. Two failures of copper condenser tubes in sea-water were due to the fact that copper is unsuitable for this purpose. Corrosion of deep-drawn brass articles was shown to be " stress corrosion." Corrosion of domestic aluminium kettles was due to inclusions of silicon in the metal, although the total silicon content was within the limit of the specification. In two cases corrosion in heat-exchangers: was due to the galvanic action of copper steam pipes on the iron tanks. Such coupling of dissimilar metals appears to be all too common in New Zealand industry. An electrical survey carried out on a heating installation in a Government building showed that corrosion experienced could not be due to stray-current electrolysis, although the potential difference between the heating pipes and nearby structures reached several volts. A start was made on the development of methods of quantitative analysis of non-ferrous metals by the polarograph, and several routine samples were analysed by this instrument. Many analyses were made of pig iron for the investigation of the smelting of ironsands at Onekaka. COAL Owing to the very large sampling programme necessitated by the coal survey undertaken on the advice of the Coal Research Committee, the staff of the Laboratory has confined its efforts largely to the making and recording of analyses of samples of coal. During the year these totalled 1,266, of which 71 per cent, were from drill-holes and were mainly supplied by the Mines Department. A further 17 5 per cent, of the samples were run-of-mine and

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