(2) Aniline Sulphate.—A solution of this is prepared by dissolving 5 parts of aniline sulphate in 100 parts of distilled water. When applied to the surface of news a yellow coloration is produced, more or less intense according to the amount of mechanical wood present. It can only be used with white papers, or papers very slightly toned.
(3) Phloroglucine.—This sensitive reagent, which gives a rose-pink colour when brushed on to the surface of the paper, is prepared by dissolving 4 grammes of phloroglucine in 100 c.c. of rectified spirits, and adding to the mixture 50 c.c. of pure concentrated hydrochloric acid.
There are several other aniline compounds which give colour reactions of a similar character, but they are not often used. The phloroglucine reagent fails as a test for mechanical wood in papers which have been dyed with certain aniline colours, for example, metanil yellow. Paper which has been coloured with this dye will, when moistened with the phloroglucine reagent, give an intense pink colour, even if no mechanical wood is present. This is due to the fact that the dye itself is acted upon by the hydrochloric acid in the test reagent. The same colour is produced on the paper with hydrochloric acid per se.
There is little difficulty in distinguishing between the colour arising from the presence of such a dye, because the effect is instantaneous, whereas the coloration due to mechanical wood develops gradually. Moreover, the reaction due to the presence of metanil yellow gives a perfectly even coloured surface, whereas with mechanical wood pulp the fibres appear to be more deeply stained than the body of the paper.
Output of a Paper Machine.—The quantity of paper which can be produced on the paper machine is readily calculated from the following data:—
| Speed of machine in feet per minute | F |
| Nett deckle width in inches | D |
| Width of sheet of paper in inches | W |
| Length of sheet of paper in inches | L |
| Number of sheets in ream | S |
| Weight of paper per ream | R |
The general formula for the output of paper per hour is
| Output in lbs. per hour = | 720 × F × D × R | . |
| S × L × W |
When the number of sheets in the ream is 480, this formula simplifies to
| Output in lbs. per hour = | 1½ × R × F × D | . |
| L × W |