<正>结合南京长江三桥铜索塔的施工测量实践，模拟现场环境进行夜间江面单向三角高程大气折光的试验研究，并对大气折光系数的变化规律进行分析，提出了利用if，知精密高差求夜间江面大气折光系数的方法。对指t?-夜间钢索塔的拼装测量。以及提高三角高程测量的精度有一定的实用价值。-

To make full use of shellac and to get the natural aleuritic acid from natural shellac, an extraction process of aleuritie acid with an important raw material synthesized civetone or dihydroeivetone in perfumery industry was developed in this paper. The fine products with a purity above 98% can be got in the process directly without any kind of organic reagent and refinery process. The influence factors, such as saponification time, saponification temperature, salting time and sodium sulfite etc., on the yield of aleuritic acid have been investigated. The results demonstrated that the yield of aleuritic acid could reach 24.64%～25.16%, and that the purity of final products could reach 98.85%～99.43G under the condition as follows: the optimal conditions were that saponification time is 96h, the proportion of NaOH 25~%in volume to shellac in weight was 6: 1, saponification temperature was 80℃, m (seedlac): m (Na2SO3) was 10 : 1; quantity of sodium sulfite, salting time, 18 h. Moreover the structure of the aleuritic acid extracted was also characterized through elementary analyzers, melting point meter, and infrared spectroscopy etc.