This is a part of the clarification; however, it is of so great and particular interest, that it deserves to be separately considered.

To conceal a remaining and undesirable tinge of yellow, the white commercial sugar is mixed in some instances with some ultramarine. It deposits from the syrup when at rest.

The admixture of ultramarine is apparently very objectionable. It is is insoluble in water and can therefore be separated by careful filtration - subsidence alone should not be depended upon. An offensive odor, sometimes experienced with plain syrups, may be attributed to the presence of ultramarine. It contains sulphur in combination, which develops sulphuretted hydrogen, the odor of which resembles that of rotten eggs, on treatment with acids. The simple syrup, which generally contains more or less invert-sugar or glucose (either originally present in the sugar, or produced by too much boiling, or even purposely inverted by the inversion process), sometimes acquires an acid reaction, due most likely to products caused by a species of fermentation. The free acid of the syrup or admixtures of fruit acids reacting on the sulphide present would generate sulphuretted hydrogen, which, if present even in minute quantity, would make a comparatively large volume of syrup offensive to the smell. Tests for the presence of sulphur (see page 590) ought to be applied by the careful bottler before using the sugar.