1. A REAGENT IN DRY SOILD FORM FOR SEMIQUANTITATIVELY ESTIMATING THE CALCIUM CONTENT OF BODY FLUIDS COMPRISING OXALIC ACID AND AMMONIUM OXALATE IN THE PROPORTION OF ABOUT 25-40 PARTS BY WEIGHT OF OXALIC ACID TO 25 PARTS AMMONIUM OXALATE, A BUFFER ADAPTED TO MAINTAIN A PH IN THE RANGE BETWEEN 2.8 AND 5.5 WHEN THE REAGENT IS ADDED TO THE FLUID TO BE TESTED, SAID BUFFER BEING THE COMBINATION OF: (A)M A MENOALKALI METAL SALT OF AN ACID SELECTED FROM THE GROUP CONSISTING OF PHOSPHORIC ACID, MALEIC ACID, MALONIA ACID AND SUCCLNIC ACID; AND (B), A MONOALKALI METAL SALT OF AN ACID SELECTED FROM THE GROUP CONSISTING OF PHTHALIC ACID, GLUTARIC ACID, ITAACONIC ACID, MALIC ACID, PIMELIC ACID AND PYROTARTARIC ACID, AND A PH INDICATOR ADAPTED TO PRODUCE A PREDETERMINED COLOR WHEN THE PH OF THE FLUID TO BE TESTED, AFTYER ADDITION OF REAGENT, EXCEEDS PH 5.5.