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Subject
- United States. Department of Agriculture286
- United States. Bureau of Chemistry and Soils285
- Nitrogen fertilizer industry259
- Nitrogen--Fixation206
- Scientific apparatus and instruments170
- Employees91
- Machinery54
- Laboratories47
- Furnaces32
- Blast furnaces22
- Fertilizer industry--Equipment and supplies19
- Glassware14
- Fertilizers--Testing10
- Radioactive substances8
- Chemical reactions7
- Chemists7
- Radioactive substances--Testing6
- Thermostat6
- Hignett, Travis P.5
- Phosphoric acid5