The per cent of total solids in tomato pulp may also be ascertained from the index of refraction of the liquor prepared by filtering the pulp as shown in Table 5; or it may be calculated from the immersion refractometer reading by the following formula, which is derived from Table 5: Per cent Solids in Pulp = 0.289(scale reading of filtrate - 15) - 0.0185(scale reading - 26.4). If the index of refraction of the filtrate has been determined by means of an Abbé refractometer, the per cent of solids in the pulp may be calculated by the following formula: Per cent Solids in Pulp = 748(n_{D} - 1.3332) - 25.5(n_{D} - 1.3376). It is of interest to note that the relation between the index of refraction of the liquor obtained by filtering tomato pulp and the per cent of solids in that liquid is very similar to the relation between the index of refraction and dissolved solids in beer and wine extract, as shown in the table prepared by Wagner.[12] [12] “Ueber quantitative Bestimmungen wässeriger Lösungen mit dem Zeiss-schen Eintauch-refraktometer,” Table XVII. In the formula given above, as well as in Table 5, it is assumed that salt is absent. If it be desired to calculate the percentage of solids in a sample containing salt from the index of refraction of the filtrate, it is necessary first to determine the amount of salt present and make correction therefor (see p. 34). For this purpose the table of Wagner[13] may be employed. The correction of the immersion refractometer reading amounts to 0.45 for each tenth per cent of salt present. [13] _Ibid._, Table I. This correction is necessary if the percentage of solids be determined by drying, or calculated from specific gravity. Determination of Insoluble Solids Transfer 20 grams of the pulp to an eight-ounce nursing bottle, nearly filled with hot water, mix by shaking, and centrifuge until the insoluble matter is collected in a cake in the bottom of the bottle. Transfer the supernatant liquor onto a double, tared filter paper covering the bottom of a Büchner funnel, using suction to facilitate filtration. Again fill the nursing bottle with hot water, stir the cake of insoluble solids so that it is thoroughly mixed with the water, centrifuge, and decant the supernatant liquor on the filter. Repeat the centrifuging and the filtration of the supernatant liquor once more, and then finally transfer the insoluble solids to the filter paper and thoroughly wash with hot water. Dry the paper and insoluble solids, and weigh. The insoluble solids are quite hydroscopic and the weight must be taken quickly. Determination of Sugar The sugar of tomatoes is probably always present as invert sugar. If cane sugar is ever present in the raw product it is doubtless inverted during the concentration of pulp. The per cent of sugar given in Tables 2 and 3 was determined by the method of Munson and Walker.[14]