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The ternary system of K 2 SO 4 + KH 2 PO 4 + H 2 O at (298.15 and 333.15) K was investigated by the method of isothermal solution saturation and moist residues. Thus the solubility data of the system were obtained, and phase diagrams of K 2 SO 4 + KH 2 PO 4 + H 2 O at (298.15 and 333.15) K were constructed on the basis of the solubility data. The solid phase in the system mentioned above was also identified. The crystallization field of potassium sulfate and potassium dihydrogen phosphate (KDP) were determined, and the crystallization field of potassium sulfate was larger than that of potassium dihydrogen phosphate. The density of saturated solutions for the systems studied at (298.15 and 333.15) K was also measured. The solubility data, density, and the phase equilibrium diagrams for the ternary system can provide the fundamental basis for the preparation of potassium dihydrogen phosphate in potassium sulfate and potassium dihydrogen phosphate aqueous mixtures.

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A total of six giant gasfields each with proven reserves of more than 100 billion cubic metres are present in the Ordos and Tarim Basins, China. The gasfields are Sulige, Yulin, Wushenqi, Da'niudi and Jingbian in the Ordos Basin, and Kela 2 in the Tarim Basin. In this paper, we report on the geochemical characteristics of the natural gas at these fields based on studies of gas composition (150 samples), together with stable isotope data (143 samples) and helium isotope data (21 samples). Results show that the gases have high contents of C 1-4 alkanes (generally over 90%) and minor contents of CO 2 (below 3%). The generally high δ 13 C values of C 1 -C 4 hydrocarbons indicates a significant contribution from humic source rocks such as Permian-Carboniferous and Mid-Lower Jurassic coal measures. δ 13 C 1 , δ 13 C 2 , δ 13 C 3 and δ 13 C 4 values for gases in Upper Palaeozoic reservoirs were -35 to -32‰ , -28 to -24‰ , -27 to -24‰ , and -23.5 to -22‰ , respectively. The δ 13 C iC4 value is higher than that of the δ 13 C nC4 .He 3 / He 4 ratios vary from 10 -7 to 10 -8 , indicating that the helium is of crustal (as opposed to mantle) origin. The CH 4 / He 3 ratio is 10 10 --10 11 , indicating that the CH 4 is of biogenic origin. None of the data is consistent with an abiogenic origin for gas in the Ordos Basin. Alkane contentBased on an analysis of 150 samples from the gasfields studied, frequency histograms of the gas's composition were constructed (Fig. 2). The figure shows that the natural gases are dominated by C 1-4 alkanes with contents over 90%. The content of methane and C 2-4 alkanes is variable. The methane