Abstract
The previous experiment showed the following possibility: the wash cement may be applicable to the coating material of freshwater tank, if we have some practical methods of preventing the alkalization of water. Calcium hydroxide dissolved from cement coating is thought to be the main ingradient of alkalization of water in tank. This suggests that it may be one of the inexpensive and practical methods to apply dry ice to the present purpose. A series of experiment was, therefore, conducted in an attempt to find the relation of pH value of water stored in tank coated with wash cement to either the lapse of time from coating to dry ice supply, the amount of dry ice supplied, or the lapse of time tightly-closed. The results obtained are summarized as follows: 1. The pH value of water in dry ice treated tank rose gradually with lapse of time after filling of water. 2. Water in tank treated 12 hours after coating showed always lower value of pH (not higher than 9.0) than any other case (after 3, 6, 9, and 24 hours). 3. The amount of carbon dioxide needed to congeal 1kg of wash cement is estimated to be about 240g. But attention should be paid to the following result: This expected value was too small to get good result and the lowest value of pH was observed in the tank treated by dry ice three times as much as the expected value. 4. The pH value of water stored in tank differed with the lapse of time tightly-closed before filling of water: as early as 12 hours after filling, the water filled in tank six hours after dry ice supply exceeded the permissible range of pH for drinking, but the water filled 48 hours after dry ice supply was kept in the permissible range of pH as long as 24 hours.5. Water stored in dry ice treated tank was good for drink with respect to all the items except pH value. 6. It may be said that application of 750g of dry ice per 1kg of wash cement could counteract, in some extent, the alkalization of water (water filled…pH 6.7, stored one day in treated tank…pH 8.9, control…pH 10.6), although this was still insufficient (permissible range…pH 5.8 to 8.6).
