Page:Paper and Its Uses.djvu/118

106 {|
 * Weight of crucible
 * 6.25
 * gm.
 * | Weight of paper
 * | 1.00
 * Weight of crucible and ash
 * | 6.365
 * | Deduct weight of crucible
 * 6.25
 * | Weight of ash
 * colspan="2" | .115 × 100 = 11.5 per cent.
 * }
 * | Deduct weight of crucible
 * 6.25
 * | Weight of ash
 * colspan="2" | .115 × 100 = 11.5 per cent.
 * }
 * | Weight of ash
 * colspan="2" | .115 × 100 = 11.5 per cent.
 * }

The ash, if not required for subsequent examination, can be thrown away, the crucible wiped out and weighed again to check the net weight of ash. It is usual to calculate the whole of the ash as added mineral water, although all fibrous materials have ash of some weight, e.g., cotton 12 per cent, esparto 3½ to 5 per cent. A delicate balance with weights from 50 gm. to 1 mgm. is advised for exact results.

Fibre Composition. It is necessary to exclude mechanical wood from most papers, and its detection is rendered easy by the use of certain solutions. A solution is made up of 1 gm. of phloroglucine in 50 c.c. of rectified spirit with 25 c.c. of concentrated hydrochloric acid added. If a drop of this solution is placed on paper in which mechanical wood is present an intensely red coloration will follow. The amount of mechanical wood may be estimated by the depth of colour, but this is very difficult, as may be proved by comparing the results obtained on papers containing 40 and 70 per cent, of mechanical wood respectively. Some aniline colours are altered in colour by the acid of the solution, although the colour is not the same as that given by mechanical wood, and it appears and fades in a different manner. A solution of 2 per cent, of aniline sulphate (1 gm. in 50 c.c. of water) will give a yellow coloration in the presence of mechanical wood. As wood fibres, jute, and some other fibres which have not been thoroughly cleaned, give colour reactions as though mechanical wood were