tailieunhanh - Humic Matter in Soil and the Environment: Principles and Controversies - Chapter 2

BẢN CHẤT VÀ PHÂN PHỐI VẤN ĐỀ Humic 2,1 KHÁI NIỆM VÀ BỐI CẢNH LỊCH SỬ Các khái niệm lịch sử Humic vấn đề theo quy định trước đó là sáng tác của một loạt các chất có thể thu được bằng cách phân đoạn trên cơ sở hòa tan trong các dung dịch kiềm và tính axit. Các chất humic đầu tiên cô lập được các hợp chất hòa tan trong các căn cứ dung dịch axít, và nước. Họ được trích xuất ở Thụy Điển Berzelius (1839), người được giao họ tên của các axit crenic và apocrenic, các. | CHAPTER 2 THE NATURE AND DISTRIBUTION OF HUMIC MATTER CONCEPTS AND HISTORICAL BACKGROUND Historical Concepts Humic matter as defined earlier is composed of a variety of substances that can be obtained by fractionation on the basis of their solubility in alkaline and acidic solutions. The first humic substances isolated were compounds soluble in bases acid solution and water. They were extracted in Sweden by Berzelius 1839 who assigned them the names of crenic and apocrenic acids the fulvic acids of today. This investigation was continued by Mulder 1840 a former student of Berzelius who in the following years isolated additional humic fractions. On the basis of color and solubility Mulder 1862 classified them into 1 crenic and apocrenic acid the yellowish to brown fractions soluble in water 2 ulmic acid and humic acid the brown and black fraction respectively soluble in alkali but insoluble in acid and 3 ulmin and humin the fractions insoluble in alkali acid and water. Mulder s accomplishment was followed twenty-seven years later by the discovery of hymatomelanic acid isolated by Hoppe-Syeler 1889 as the ethanol-soluble fraction of humic acid. Since then no Copyright n 2003 by Marcel Dekker Inc. All Rights Reserved. further achievements of major importance can be noticed in the study and isolation of humic substances until Oden s 1914 1919 concept surfaces at the start of the twentieth century. Considered by many scientists as based on a more solid scientific foundation it is in essence a revision of Mulder s classification. Oden recognizes 1 fulvic acid which replaces the use of the terms crenic and apocrenic acid 2 humic acid for the fraction soluble in alkali and insoluble in acid 3 hymatomelanic acid a name used earlier by Hoppe-Syeler 1889 for the humic acid fraction soluble in ethanol and 4 humus coal for replacing humin and ulmin. Concepts in the Early Twentieth Century Oden s theory though challenged many times during the years has set the .