Method of making plaster of paris product

Claim 1

A PROCESS FOR MAKING A SETTABLE PLASTER OF PARIS PRODUCT FROM PLASTER OF PARIS, COMPRISING A MINOR AMOUNT OF ALKALINE IMPURITIES LESS THAN SIX PER CENT BY WEIGHT COMPRISING THE STEPS: OF FORMING A SUSPENSION OF SAID IMPURE PLASTER OF PARIS IN WATER AND OF A WEAK ACID AS TRANSITORY RETARDER THEREFOR AND SELECTED FROM THE GROUP CONSISTING OF ACETIC ACID, FORMIC ACID AND PROPIONIC ACID; ADDING TO SAID SUSPENSION A MINOR AMOUNT OF A STRONG ACID, NON SUBSTANTIALLY IN EXCESS OF THE AMOUNT EQUIVALENT STOICHIOMETRICALLY TO THE AMOUNT OF SAID IMPURITIES IN SAID PLASTER, AND SELECTED FROM THE GROUP CONSISTING OF ORGANIC ACIDS, STRONGER THAN FORMIC ACID, THAT FORM CALCIUM SALTS THE WATER SOLUBILITY OF WHICH DOES NOT EXCEED ONE GRAM PER ONE HUNDRED CUBIC CENTIMETERS OF WATER AT TWENTY DEGREES CENTRIGRADE, AND OF THE INORGANIC ACIDS STRONGER THAN FORMIC ACID; AND DRYING SAID PLASTER OF PARIS AT ELEVATED TEMPERATURE, THEREBY REMOVIING SAID WATER AND SAID TRANSITORY RETARDER AND FORMING SAID SETTABLE PLASTER OF PARIS PRODUCT.