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Langheld
Chemische Berichte, 1910 , vol. 43, p. 1858
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Langheld; Oppmann; Meyer
Chemische Berichte, 1912 , vol. 45, p. 3758
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Langheld
Patent: DE248956 ;
Fortschr. Teerfarbenfabr. Verw. Industriezweige, vol. 11, p. 1146