About: http://webisa.webdatacommons.org/353529280

Property	Value
http://www.w3.org/1999/02/22-rdf-syntax-ns#type	http://www.w3.org/ns/prov#Entity
http://www.w3.org/ns/prov#value	Examples of such systems might be thymolphthalein (blue) or phenolphtholein (red) dissolved in a suitable alkaline vehicle as the marking liquid; and the eraser or anti-marking liquid could be such reagents as citric acid or acetic acid.
http://www.w3.org/ns/prov#wasQuotedFrom	google.es