1. C. W. Georgi, Motor Oils and Engine Lubrication, Reinhold, New York (1950).
2. J. Guttenberger and M. Marold, Z. Anal. Chem.,262, No. 2, 102 (1972).
3. J. Nouman, Talanta,19, No. 10, 1202 (1972).
4. P. J. Brewer, J. Inst. Pet.,58, No. 559, 41 (1972).
5. S. A. Gabsatarova, O. L. Glavati, I. L. Rabinovich, et al., Neftepererab. Neftekhim. (Naukova Dumka, Kiev), No. 11, 7.