One of the present authors, S. Nagai, studied already on various mixed Portland cements and reported them (Journ. of Soc. Chem. Ind., Japan, 1929, 32, 343, 629, 838, 971, 1171; 1930, 33, 279, 601; 1931, 34, 461). The studies were further continued by the present authors and some results were preliminary reported in the present paper. The brief summany from the original Japanese report is abstracted as follows:
(1) The natural siliceous raw material “Hakusan Kasanbai or Yokeihakudo” of tuff origin was mixed with clinker in various proportions and ground with gypsum by a laboratory ball mill.
(2) The chemical composition of raw materials and the prepared Portland cement and mixed Portland cements are compared in the following table.
(3) These cements have the following physical properties of specific gravity, fineness, voids, etc., which are shown with the mixing proportions of their raw materials in the following table.
(4) The samples were tested on their strength of 1:3-cement-sand mortars by the method described in the specification of Japanese Engineering Standards for Portland cement and blast furnace cement (JES 28 and 29), and the following results were obtained.
(5) The cement samples were also tested on the compressive strength of plastic mortar by the special small cylindrical test piece, which was proposed by the present author (S. Nagai: “Studies on cements by the plastic mortar of small cylindrical test piece”, Journ. Soc. Chem. Ind., Japan, 1929, 32, 635, 641; 1930, 33, 129, 290) and obtained the following results.
These results by the plastic or wet mortars of high water cement ratio are better to discuss on the mixed Portland cements than those by the dry mortars adopted in specifications of all countries. The principles of this plastic mortar tests are nearly equal to those proposed by Prof. Ros: “Die zukuenftigen schweizerischen Normen fuer Bindemittel auf Grundlage von Untersuchungsergebnissen der E. M. P. A. der E dg. Tech. Hochschuele in Zuerich, Diskussionsberichte Nr, 1, Nr. 10 & Nr. 60” and Dr. G. Haegermann: “Die Pruefung plastischer Moertel”, Protokoll des Vereins Deutscher Portlandzement-Fabrikanten, Sept. 1929 and “Die Zementpruefung bei Anwendung von Moertel mit hochem Zementzusatz”, Reports of the New International Association for Testing Materials, 1931.
These studies are now further being continued and will be reported hereafter.

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On the MgO content in Portland cement were studied by several investigators, i.e. A. A. Klein, Tonindustrie Zeitung, 46 (1922), 663. K. Balthasar, Tonindustrie Zeitung, 49 (1925), 277; Tonindustrie Zeitung, 56 (1932), 1016. S. Kondo and T. Wada, This Joural 40 (1932), 769. etc.
The authors have known that the MgO content can be safely allowed up to about 8% from these results. However, the above athors' experiments were at a distance from practical preparation. Therefore we have carried out these experiments by using practically prepared raw materials.
(1) MgO content varied 3-17%, Hydraulic modulus=2.15, for 5 clinkers.
(2) MgO content, being kept at 10% and Fe₂O₃ contents increased, Hydraulic modulus=2.00 for 2 clinkers.
(3) MgO content varied 6-7%, Hydraulic modulus=2.25, Iron modulus=1.70, for 2 clinkers.
These raw mixtures were burnt in a rotary kiln (40×55×700cm.) with heavy oil.
The clinkers and cements were tested by the ordinary testing method. Results are as follows.
(a) The burning of raw mixture grows the more easily according to increase of MgO content.
(b) In group 1, that containing 3% MgO has shown the most strength on tension and compression of 1:3 mortar. In group 2, the clinkers have sintered more easily than others. In group 3, the boiling test of pats are unsoundness.
(c) Conclusion: The MgO content can safely allowed up to 12%.

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That glasses melted by passing electric current through their batches are colored black by the contamination of electrode-carbon and also that the discoloration can be avoided perfectly by introducting a few per cent of zinc oxide to the batches were described in the first report (this jour., 1932, 40, 72).
Then the authors made a study of the material of the electrodes with a result that Acheson graphite was most promising for the purpose.
In the present paper the results of experiments made of the reaction temperatures of zinc oxide and amorphous carbon or artificial graphite are given. The temperatures were determined by thermo-balance method and also by thermal analysis method.
Chemically pure zinc oxide, sugar carbon, and 99.5% pure artificial graphite were used. The samples were heated in a current of nitrogen in electric furnaces whose temperatures were raised with constant rates.
General conclusions are that the temperatures given by the thermal analysis method are higher than those given by the other and also that the amorphous carbon reacts with zinc oxide at a temperature about 50°C lower than the graphite, as shown in Table 1:

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