The methods which have been used for the determination of zinc in water are not adequate in the sensibility and procedure. It was found that the application of zincon (2-carboxy-2'-hydroxy-5-sulfoformazyl-benzene) introduced by Yoe and Rush is most suitable for the determination of zinc in water. Copper also forms a blue complex with zincon. Good result was obtained by the addition of 1 g of thiourea for masking 100 μg of copper presented with 10μg of zinc. In the presence of much iron (III), aluminium, copper and mercury (II), it is necessary to extract zinc from a weakly ammonical solution with dithizon-CCl₄ solution, and to shake the extract with dilute HCl (0.02 N) to bring zinc into the aqueous phase.

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A new colorimetric determination of micro-quantities of chloride ion by use of mercurous molybdate is described. 10 ml of sample solution containing less than 40 μg/ml of chloride ion is treated with 1 ml N-HNO₃ and 0.1 g mercurous molybdate, stirred for 10 minutes. After the solution is filtered off, 5 ml of the filtrate is treated with 1 ml of 2% thioglycolic acid and the light absorbancy of colored solution is estimated at 360 mμ.

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This paper is described the method of measurement of organic substance contained within air-borne dusts, using the oxydative reaction by silber bichromate. In the determination of organic substance, sampling technique is used Katz's method, and residual bichromate is determined by photoelectric method. The result as follows : The contents of organic substance of the particles due to smog and tobacco smoke are the highest, and the deposited particles in residences, department stores and others are higher than that of the surface earth particles, and the contents of accumulated earth particles are the lowest.

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The present paper is described the rusults obtained by investigation of houry variations of air-borne dusts concentration and bacterial counts indoors and outdoors and the differences at the places, using several estimation methods. The concentration of air-borne dusts and bacterial counts indoors depend upon the artificial factors in the room and the atmosphere. The magnitude of houry variations of the concentrations of the air-borne dusts are often larger than that of those seasonal variations and regional differences on the average. No significant differences are not found between the dust counts determined indoors and outdoors using the Roken dust sampler. Therefore, it is known that these values chiefly depend upon air-borne particulates owing to the air pollution, and is not intensely affected by artificial pollution in the rooms. On the otherhand, the values of dusts and bacterial counts by means of electrostatic dust sampler and bacterial sampler are intensely affected by artificial pollution in the rooms, and these values indoors generally do not have relation to the values outdoors.

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