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The samples received are an indication of the amount of service work carried out. The number received during 1949 (31,004) was slightly less than in 1948 (31,677). The work done for the Department of Health decreased by about 2,000 samples, mainly milk samples in the two South Island districts. In addition a great deal of time was spent by professional officers in answering chemical and chemical-engineering inquiries, in serving on technical committees, and assisting other Departments with professional advice on their problems. DISTRICT LABORATORIES The work of the district laboratories is not shown separately, but is included under the subject headings; they have continued to provide services dealing mainly with foods, drugs, toxicology, gas-testing, analyses, general advisory work, industrial investigations, &c. Each of these laboratories is under the charge of a Government Analyst, and has a staff of four to six chemists and the necessary non-professional staff, which includes four or five technicians. ROCKS, MINERALS, AND CLAYS Practically all of this work is concentrated in the "Wellington Laboratory. It comprises analyses and investigations of silicate and other minerals for the Geological Survey, Soil Bureau, Pottery and Ceramics Research Association, and Mines and various other Government Departments. In the absence of a section of the Laboratory to deal specifically with building-materials, problems of cement, concrete, concrete aggregates, and concrete products were handled in conjunction with the rock and mineral work. A senior officer returned towards! the end of the year from a course of study in radio-chemistry lasting fourteen months, during which he visited institutions in the United States of America, Canada, and England. Training was obtained in the techniques used for the handling of isotopes, both radioactive and stable, for use in medical and biochemical problems. The information and experience gained will be of the greatest assistance in the research on these matters which will be carried out in New Zealand. Analyses were made of titanomagnetites separated magnetically by the Dominion Physical Laboratory from North Island black sands. The residues were also further fractionated magnetically in a search for ilmenite. A well-equipped laboratory was set up at Onekaka to carry out urgent analyses for the ironsmelting experiments that were made by the Department of Industries and Commerce. Both at Onekaka and at "Wellington numerous urgent analyses of sinters and slags were made in connection with the experiments. An investigation was made of materials collected by the Geological Survey from Oamaru, Canterbury, Te Kuiti, and other districts in relation to their use in the manufacture of cement. For the Ministry of Works further investigations were made of rock materials suggested for use as aggregates in concrete for hydro-electric dams on the Waikato River. The chemical method was again used for attempting to evaluate the potential reactivity of rock aggregates with high-alkali cement which may lead to deterioration of concrete, and this method was supplemented by Stanton mortar-bar tests in which the expansion of bars of concrete made under prescribed conditions and stored in closed containers over water in a constant-temperature room is measured from time to time. While the

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