Henry's law pointed out that the solubility coefficient of oxygen is very low. This means that only small amounts of oxygen are dissolved in the plasma. Consequently, about 98% of the oxygen in the blood must be transported within erythrocytes where it attaches to the iron within hemoglobin molecules. Oxygen bound to hemoglobin is referred to as oxyhemoglobin. Hemoglobin without bound oxygen is called deoxyhemoglobin.