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Before rock phosphate was available for superphosphate manufacture, animal bones were used. They were collected from local freezing works, ground up, and treated with sulfuric acid.
Te whakamahi i tēnei tūemi
Archives New Zealand - Te Rua Mahara o te Kāwanatanga
Reference: AANR 6329 26 DA 32815
Permission of Archives New Zealand Te Rua Mahara o te Kāwanatanga must be obtained before any re-use of this material.