中文摘要：

利用比重瓶法对火山喷出物发育土壤的比重进行测定,结果表明：玄武岩质火山喷出物发育土壤的比重大于粗面岩质火山喷出物发育土壤的比重;基于粒径小于1 mm土粒测定的比重,玄武岩质火山喷出物和粗面岩质火山喷出物发育土壤的比重均小于一般土壤的平均比重2.65 g cm~（-3）;基于粒径小于0.1 mm土粒测定的比重,除个别玄武岩质火山喷出物发育土壤外也小于2.65 g cm~（-3）。分别取比重值为2.65 g cm~（-3）、粒径小于1 mm土粒的实测比重和粒径小于0.1 mm土粒的实测比重,计算不同粒级土粒的沉降时间,并进行颗粒组成的实验研究表明：取不同比重值测定的土壤颗粒组成含量相差较大而且影响土壤质地定名。由于成土母质的矿物组成决定土壤的比重,且土壤颗粒组成的静水沉降实验是在粒径小于0.1 mm土粒的悬液中进行的,所以,准确测定土壤颗粒组成含量,需要区分成土母质的矿物组成,并测定其小于0.1 mm粒径的土粒比重,重新计算沉降时间。

英文摘要：

This paper measured the specific gravity of soil developed from volcanic ejeeta with pycnometer method. The experiment results showed that the specific gravity of soil developed from volcanic ejecta was higher than that developed from trachyte ejeeta. For soil developed from basaltic volcanic ejeeta and trachyte volcanic ejecta, its specific gravity was less than 2.65 g cm-3 （average specific gravity of general soil） when soil particles size was less than 1 mm and 0.1 ram. Then we separately collected soil particle with 2.65 g cm-3, specific gravity, or that with measured values for less than 1 mm or 0.1 ram, calculated the settling time for different soil particle sizes, and did the experiments about particle composition. The results showed that the contents of soil particle composition varied widely between in soil particles with different specific gravity, which affected the name of soil texture. Mineral composition of soil parent material affected soil specific gravity, and hydrostatic settlement experiment of soil particles was done in soil suspension less than 0.1 mm particle, so when the composition of soil particles was accurately measured, it was needed to distinguish the mineral composition of soil parent material, determined specific gravity of soil particles less than 0.1 mm size, and then recalculated the setting time of soil particle.