While occlusion of the elements in the carbonaceous ash residue has been found to be a problem, calcium is more readily extracted from the black ash containing 11% carbon than from the light gray, carbon free ash ofCucurbita maximaandCucurbita andreanaembryos. The temperature of 600° C seems to be the point at which a change in the ash occurs. At and above 600° C ash samples require additional digestion with dilute nitric and hydrochloric acids before giving the correct calcium levels. Plant materials such as NBS Tomato Leaves and Wheat Flour standards do not show a change in ash solulility at higher ashing temperatures.