24,22=7; 24,47=8; 26,30=11; 27,26=13; 28,15=16; 28,16=15; 28,19=14; 29,27=18; 29,38=19; 31,44=21; 32,7=22; 32,26=26; 32,35=24; 32,52=25; 33,34=27; 33,51=28; 35,7=30; 35,33=31; 53,47=32; 35,55=33; 35,56=34; 36,8=35; 36,35=36; 37,8=37; 39,3=39; 40,3=41; 40,34=43; 40,35=44; 41,20=45; 42,10=48; 42,18=49; 43,8=52; 44,24=54; 45,22=56; 45,25=57 von:
Pennsylvania State College. Mineral Industries Experiment Station: Mineral Industries Experiment Station bulletin (SLUB)