Show why rosin in paper boscn Is used in the manufacture of paper to make it water resistant so that it will be resistant to writing ink for this purpose common rosin to Is treated with soda a rosin soap being formed which Is a combination of sodium and free rosin and which Is soluble in water this material to la added dad to the paper stock in the form of a dilute solution in water aluminum minum sulphate Is then added to the paper stock this precipitating the rosin la in very finely divided form tile the precipitate consisting consisting of a mixture of aluminum resl nate and free resin which when the paper sheet Is dried forms forma a wilter proof film over the paper fiber |