The rate of hydration of hardened cement pastes can be well expressed by means of the volume of hydrates in unit volume of hardened pastes. This is calculated by the following formula,
V_h=l(1+1/sp)m
where,
V_h: the volume of hydrates in unit volume of the pastes.
l: weight of cement in the pastes.
m: amount of combined water in the pastes in wt. per unit wt. of used cement.
p: amount of water necessary for perfect hydration in wt. per. unit wt. of used cement.
s: specific gravity of used cement.
From author's experiment, the following results are ascertained.
(1) Under earlier age than 28 days, increase in the rate of hydration of the pastes of a fixed water cement ratio is proportional to logarithm of the age. The state of increase is approximately the same within the limits of water cement ratio from 0.4 to 1, 0, but in the case of 0.3 water cement ratio, increase of the rate of hydration is somewhat smaller than other cases at longer age than 28 days.
(2) In the case larger water cement ratio taan 0.4, the rate of hydration decreases as initial water cement ratio increases, and also it decreases linearly as true water cement ration (total water contents in hardened pastes) increases.
(3) The rate of hydration is not the same as varieties of cement, and the difference between them is remarkable especially in earlier ages.
(4) The effect of low temperature curing on the rate of hydration is more considerable, earlier the age, and larger the amount of water used. The rate of hydration is remarkably accelerated by not water curing even in a short time.
For example, the pastes of 0.3, 0.4, 0.5, 0.65, 1.0 water cement ratio which had been cured in hot water of 99°C and 70°C during six hours after one day ordinary curing, have been all accelerated about to 70% as compared with ordinary curing.

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(1) Supplementing the discriptions of the previous paper concerning the geographical distribution and occurrreuce of diatomaceous earth in Japan, the details of actual survey accomplished by the anther on several deposits located in Karafuto and Hokkaido are reported in this paper.
(2) The deposits in Karafuto are discovered only in south region, the districts along Rutaka, Taranai, Amaryu and Suzuya rivers. The chief deposit that occur along the Rutaka river lies under a thin and narrow layer having an average thickness of 70cm, and showing different strata from any others so far discovered in tertiary at Hokkaido. These facts suggest that the deposit in Karafuto may have been originated fresh water or semi salt water sinking their frustules to the bottom of lake or bay, probably in quaternary.
(3) Their are more than a dozen of diatomaceous earths in Hokkaido. Their deposits are located in Kimobetsu, Abuta district; Setana district; Yobito and Notoro, Abashiri district; Kabaoka, Soya district; Otoshibe and Kumadomari, Kayabe district; Yamasedomari, Kameda district; and Tatesawa Hiyama district.
The quaternary deposits in Hiraoka, Kimobetsu, Abuta district are situated 25km. north-east of the city of Kutchan and occur as small and shallow beds of 60cm. in thickness, covered by about 1m. of ovgrburden. The earth is especially pure and free of contamination showing 90 per cent of soluble silica and is consisted with whole frustles of epithemia and other diatoms of fresh water, without any of marine types.
On the contrary, the other deposits, those belonging to the tertiary formations, occur as solid and compact massive beds with contamination of impurities such as clayey and organic matter showing a striking difference with any others of quaternary.
View of outcrops of their deposits and states of minning in proceed are shown in photographs.

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