Two ksinds of dolomite plasters,(a) three samples of cover coating dolomite plasters and (b) two samples of under coating dolomite plasters were tested without or with addition of 3, 5, 10 or 15% of gypsum plaster of calcined hemihydrate (CaSO₄·1/2H₂O) on their hardening shrinkage, strength, and shrinkage cracks. The addition of 10-15% of calcined gypsum plaster was determined to be decidedly effective to improve the properties of calcined dolomite plasters of both under and cover coating uses. The shrinkage and its cracks of simple dolomite plaster were completely diminished by the addition of 10-15% of calcined gypsum plaster. The degrees of whiteness of these plasters were measured and compared with the standard whiteness and determined that these simple plasters of gypsum plaster, cover coating dolomtie plaster and gypsum-dolomite plaster were superior to the stadard whiteness, but the under coating dolomite plaster was inferior to the standard whiteness. The surface hardness of ha rdened plasters of these simple dolomite plaster and gypsum-dolomite plaster is now being further studied from several points.

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In continuing the previous report (Part 1), the authors reported the studies on the methods of manufacture of basic magnesium carbonate by reaction of magnesium hydroxide, sodium hydrogen carbonate and condensed bittern (magnesium chloride solution).
The transparent degrees of basic magnesium carbonate (per same volume mixed solution of nitrobenzene and benzene) were excellent as additional amounts of Mg (OH) ₂ wexe used 1.5-2.0 times the theoretical amount per 2NaHCO₃ and MgCl₂.
In this report (Part 2), additional amounts of Mg (OH) ₂ are used 0-1.5 and 2.5-4.0 times the theoretical amount
As the results of these experiments, thechemical composition of basic magnesium carbonate,(Mg: CO₂), change (5:4)-(4:3)-(3:2)-(2:1), according as increase additional amounts of Mg (OH) ₂.Basic magnesium carbonate which has the chemical composition (4:3)-(3:2) shows excellent transparent degree.

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The removal of CaSO₄ by means of sodium oxalate was completely and the sodium oxalate was recovered by decomposition of calcuim oxalate which was obtained by the reaction of sodium oxalate and calcium sulfate, by means of soda ash being its recovering yield about 97%.

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The application of electrophotometer was studied for the determination of SO₄" in salt, sea water, brine and bittern. The results are summarized as follow;
1) The penetration optical intensity of BaSO₄ suspension was affected by the aging time affter addition of reagent, when the suspension was made by adding powdered BaCl₂. The intensity will become stable in two hours. The most accurate estimation may be got in this method by measuring the intensity at immediate or at two hours after the addition of reagent. When the suspension was maee by adding BaCl₂ solution, the the optical intensity did not vary by aging and in this method the measarment will be done after 5 minutes.
2) Fo the determination, of SO₄" in salt; sea water, brine arnd bittern the estimation curves, made with corresponding samples, must be used and the errors in this method may be less than 4%.

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Vol. 6 (1952) No. 5 p. 202-209

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