The results by this method are only approximate, but are sufficiently accurate for manufacturing control. Table 12 gives a comparison of the solids obtained by drying in vacuum at 70° C. with results obtained by the refractometer. TABLE 12.—_Solids in Ketchup Obtained by Drying in Vacuum at 70° C. and by Abbé Refractometer from Geerlig’s Table_ +------------------------------+ | Solids in tomato ketchup | +----------------+-------------+ | By drying in | By Abbé | |vacuum at 70° C.|refractometer| +----------------+-------------+ | _Per cent_ | _Per cent_ | | 29.5 | 29.0 | | 30.0 | 29.4 | | 32.8 | 32.4 | | 28.0 | 27.9 | | 22.0 | 21.8 | | 27.7 | 28.0 | +----------------+-------------+ There are several errors in this determination which partially compensate for each other and give results fairly comparable with those obtained by drying. The refractometer of course determines only soluble constituents. Since salt gives a higher refractive reading than the same per cent of sugar, and since tomato solids give a higher refractive reading than the same percentage of sugar, and since any acetic acid of the vinegar is also read as solids on the refractometer, the total increase in reading due to these different factors nearly compensates for the insoluble solids of the ketchup. The variation of the per cent of solids as obtained by the refractometer from that obtained by drying will depend somewhat on the composition of the ketchup and in using the refractometer it is advisable to also determine the solids by drying on a few samples to obtain the relation between the two figures for that particular ketchup. TABLE 13.—_Refractive Index and Per Cent Solids in Tomato Ketchup_[21]