It is plain, then, that if a given quantity of the dark saccharine fluid produced by boiling--say, enough to cover ten divisions of the graduated tube, as shown in the figure--has to have added to it an equal bulk of distilled water in order to produce {215} the color of the standard solution, the tested fluid will be of the strength of two grains to the ounce; if three times, three grains; and so on; while fractional additions, as indicated by the graduated markings, would show fractional additions to the proportion of sugar.[42] [Footnote 42: A more exact comparison of the saccharine liquid with the standard is made by pouring into a flat-bottomed colorless tube six inches long and an inch in diameter as much of the standard solution as will form a column about an inch in height, and an exactly equal column of the saccharine fluid in a precisely similar tube. The operator then looks down through the two tubes at once, one being held in each hand, upon the surface of a white porcelain slab or piece of white paper. In this way slight differences of tint are easily recognized; and if the liquid to be analyzed is found darker than the standard, it is returned to the graduated tube and diluted until the two liquids are found to be identical in color, when the final reading is made.] The presence of albumen, even in considerable amount, has but little effect upon the test, nor does the coloring matter of normal urine, according to Johnson; but he says there is a coloring matter associated with ser-albumen in albuminous urine, and with egg-albumen as well, which has a reducing action on picric acid. This is partly separated by filtering off the precipitated albumen, and entirely removed by repeated filtration through animal charcoal. So, too, the albumen removed by coagulation and filtration, if thoroughly washed, does not give any red reaction if boiled with picric acid and potash diluted in the same proportion as when testing for sugar. Neither do any other unoxidized sulphur compounds found in urine decompose the picric acid and render the test fallacious. Johnson and his son, G. Stillingfleet Johnson, claim that the picric-acid test is as accurate as any other, and that it is even more accurate than either Fehling's or Pavy's process, because the picric acid is not acted upon by uric acid or urates, which do reduce the oxide of copper. The method of analysis by the picro-saccharimeter, they claim, is at least as speedy and as easy as any other. The materials and apparatus required are easily prepared, inexpensive, and not, like Fehling's copper solution, liable to undergo rapid changes.