Dominant species distributed along the shore of the Inland Sea of Japan are Lyngbya aestuarii Liebm. and Rhizoclonium arenosum (Carm.) Kütz., and these brackish algae become the object of weeding. Under the peculior environmental conditions on the salt-field, salinity, temperature and quantity of the sea water are the main factors controlling the growth of the algae. Especially, low salinity and organic matters contained in the sea water promote the growth of Rhizoclonium and Lyngbya respectively. Among the various herbicides, CuSO₄, CuCI₂·Cu(OH)₂·H₂O, CuCO₃·Cu(OH)₂, Cu(OH)₂, 2, 4-D, PCP, NaClO solution, NaClO₂ and NaClO₂ are specially used for the algicides, and their critical density to algae and time of their treatment are examined within the range of 0.1-1,000 p.p.m. Sodium hypochlorite solution (NaCIO) is the most suitable algicides for the salt-field on account of its strong algicidal power and being non-poisonous to human bodies

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On the manufacture of Mg(OH)₂ from sea water, brine or. bitter and alkali, waste lime from acetylene generator was utilized as alkali raw material instead of slaked lime. In part 1, pilot plant and process of manufacturing Mg(OH)₂ and quality of the product were described. Results of chemical analysis of the prodct were as follows, ignition loss 34.47%, CaO 3.74%, insoluble matter for HCI 0.76%, Fe₂O₃+Al₂O₈ 1.93% and MgO 58.27%.

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Crystals of common salt are investigated by a microscope and some interresting results are found.(1) Crystals of solar salt are classified to three types according to the directions of crystal growth.(2) Relation between evaporation velocity and cavity formation (containing mother liquid)in salt crystals is considered, and there are more cavities, where evaporation velocity is great.(3) water content in salt, estimated from the volume of cavities by microscopic observation, coincides with that acquired by drying method.

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