(1) _Nitric Acid._--This produces a brown stain on the paper, but it is not a desirable reagent for ordinary office purposes. (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 720 × _F_ × _D_ × _R_ Output in lbs. per hour = -----------------------. _S_ × _L_ × _W_ When the number of sheets in the ream is 480, this formula simplifies to 1½ × _R_ × _F_ × _D_ Output in lbs. per hour = --------------------. _L_ × _W_