Five grams of the fine phosphate meal, or slag meal, are moistened in a flask of 500 cubic centimeters content with some water and boiled on a sand-bath with forty cubic centimeters of hydrochloric acid of from 16° to 20° Beaumé. The boiling is continued until only a few cubic centimeters of a thick jelly of silicic acid remain. After cooling, some water is added and the phosphate shaken until the thick lumps of silica are finely divided. The flask is then filled to 500 cubic centimeters and its contents filtered. Fifty cubic centimeters of the filtrate are treated with fifteen cubic centimeters of the Joulie solution and treated in the manner described with magnesia mixture, precipitated, ignited, and weighed. The precipitate can also be dissolved and treated with uranium solution as described. The method used by Oliveri may also be employed and it is carried out as indicated in the following description:[99] A weighed quantity of the slag is reduced to a fine powder. To five grams of the sample is added three times its weight of potassium chlorate and the whole is intimately mixed. The mixture is then placed in a porcelain dish and hydrochloric acid is added, little by little, until the potash salt is completely decomposed. It is evaporated until the mass is dry. The material is then treated with fuming nitric acid, and the determination of the phosphorus is made by the ordinary gravimetric method. By carrying on the operation as described above, a reduction of phosphoric acid is avoided, and the presence of an abundant quantity of potash prevents the formation of basic iron phosphate which is insoluble in nitric acid.