The Determination of Micro Amounts of Water in Volcanic Rocks Released during Mechanical Grinding

Abstract

The authors designed a special ball mill made of Pyrex glass for the determination of micro amounts of water released from rock sample during mechanical grinding (Fig.1). A set of balls which is made up of 4 balls of g5 16 mm, 30 balls of 13 mm and 4 10 mm, and 200 balls of 4 5 mm and rocks sample of uniform grain size (1.00 to 0.84 mm) are placed in the ball mill. The ball mill is connected with a cylinder of nitrogen gas, silicagel-P205 drying tubes, gas flow meters and a Karl Fischer titration vessel by a glass and copper pipes, as shown in Fig.2. An adsorbed water in the ball mill is expelled by passing the dried nitrogen gas. After taking off the ground glass joints a, e and f from the ball mill, the ball mill was placed on a revolving holder and rotated at 120 rpm more than two hours. When the ball mill is revolved for 120 minutes, 99.2% of 10 g of a basalt samples are pulverized to pass through a 0.044 mm (325 mesh) testing sieve. It is confirmed that con-tamination of the ball mill with the atmospheric moisture is negligibly small during a five hours run. After pulverizing the sample, the. ball mill is connected with the Karl Fiscer titration vessel in the same way as the prescribed procedure. The water released from rock sample during grinding is transported by flowing the dried nitrogen gas with constant flow rate to the Karl Fischer titration vessel and absorbed into an anhydrous mixture of methyl alcohol and ethylene glycol (1: 1). After that the mixture was titrated by Karl Fischer method. The accuracy is confirmed to be ± 0.02 mg H2O. The amounts of water released from the most usual fresh volcanic rocks and from many glassy rocks was determined to be less than 0.0001%. This value may be considered negligible. The rocks including so-called"residual magmatic water"and highly hydrated glassy rocks released large amount of water. If the water released on mechanical grinding are disregarded, the amounts of water in the rocks can not be correctly evaluated. Liparites, from Nii-shima and Kozu-shima, absorbed even an extremely small amounts of water which remained in dried nitrogen gas during mechanical grinding and analytical procedure.