Recently, “Naphtha method” by using naphtha and sodium hexametaphosphate was introduced for treatment of rocks for microfossils analysis (Maiya and Inoue, 1973). However, calcareous microfossils were found to be soluble in sodium hexametaphosphate solution in the course of disintegration. The authors investigated the dissolution effect of sodium hexametaphosphate solution on planktonic foraminifera. The experimental solution was divided into the following concentration (1.0, 0.4, 0.2, 0.1, 0.01, 0.001%). Under these experimental concentrations, binocular microscopical observations were made on the dissolution effect on planktonic foraminiferal tests at the following periods (0.5, 1.2, 4, 6, 12, 24, 48, 72 hrs).
The results obtained are as follows:
1. The dissolution of planktonic foraminifera increases in accordance with concentration of the solution as well as time within the limits of this experiment. The same result was obtained in dissolution experiment of inorganic calcium carbonate.
2. Planktonic foraminifera used in this experiment can be divided into two groups, that is, one is species to be susceptible to dissolved and the other those resistant to dissolution. Resistant species to dissolution in this experiment agree approximately with the dissolution ranking of planktonic foraminifera suggested by Parker and Berger (1971). On the other hand, susceptible species to dissolution do not always agree with that of Parker and Berger (
op. cit.). Especially,
Globigerinita is most susceptible to dissolution among species tested in this experiment.
3. It is concluded that, in “Naphtha method”, the use of sodium hexametaphosphate above the concentration of 0.01% is not suitable for treatment of rocks for microfossils analysis.
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