Sentence:  Polyphosphates gave renewed life to soap products at a time when surfactants were a threat though expensive , and these same polyphosphates spelled the decline of soap usage when the synergism between <WSD>polyphosphates</WSD> and synthetic detergent actives was recognized and exploited . 
Meaning of the word marked with <WSD> tags:  a salt or ester of polyphosphoric acid