Sentence:  Phosphorus is known to improve the strength of copper, and to make it cast soundly. Abel, chemist to the British War Department, stated before the Institute of Civil Engineers, that he had made some experiments upon the combinations of phosphorus and copper, and "had found that by the introduction of a small proportion, say from 2 to 4 per cent., of phosphorus into copper, a metal was produced remarkable for its density and tenacity, and superior in every respect to ordinary <WSD>gun-metal</WSD>. ... The experiments alluded to were merely preliminary, and had been, to a certain extent, checked by the improvements since introduced in the construction of field-guns, which had led to a discontinuance of the employment of <WSD>gun-metal</WSD>." 
Meaning of the word marked with <WSD> tags:  A type of bronze used for making cannons.