-----------+------------------------------------------------------------ Higher | Lower Density, _d._ Density, D +----+----+---+----+-----+-----+-----+---+---+-----+---+----- (Twaddell).| 12.| 11.|10.| 9. | 8. | 7. | 6. | 5.| 4.| 3. | 2.| 1. -----------+----+----+---+----+-----+-----+-----+---+---+-----+---+----- 16 |33·3|45·4| 60|77·7|100 |128·5|166·6|220|300|433·3|700|1,500 15 |25·0|36·4| 50|66·6| 87·5|114·3|150 |200|275|400 |650|1,400 14 |16·6|27·3| 40|55·5| 75 |100 |133·3|180|250|366·6|600|1,300 13 | 8·3|18·2| 30|44·4| 62·5| 85·7|116·6|160|225|333·3|550|1,200 12 | | 9·1| 20|33·3| 50 | 71·4|100 |140|200|300 |500|1,100 11 | | | 10|22·2| 37·5| 57·1| 83·3|120|175|266·6|450|1,000 10 | | | |11·1| 25 | 42·8| 66·6|100|150|233·3|400| 900 9 | | | | | 12·5| 28·5| 50 | 80|125|200 |350| 800 8 | | | | | | 14·2| 33·3| 60|100|166·6|300| 700 7 | | | | | | | 16·6| 40| 75|133·3|250| 600 6 | | | | | | | | 20| 50|100 |200| 500 5 | | | | | | | | | 25| 66·6|150| 400 4 | | | | | | | | | | 33·3|100| 300 -----------+----+----+---+----+-----+-----+-----+---+---+-----+---+----- _Antichlors._--The residues of chlorine which may be left in pulp after bleaching are frequently neutralised by the use of substances termed antichlors, which react with the calcium hypochlorite, converting it into chlorides. The sodium hyposulphite is the most frequently used antichlor, the reaction between this and hypochlorite resulting in the formation of calcium sulphate and sodium chloride; 100 lbs. of commercial bleaching powder will require 30 lbs. of crystallised sodium hyposulphite. The sulphites of soda and lime also act as antichlors, reducing the hypochlorite of calcium into sulphate of lime or soda. The chief advantage of the use of sulphites is to be found in the fact that the substances obtained by the reaction are neutral. The best practice in bleaching is to avoid the necessity for using any forms of antichlors by careful regulation of the bleaching process. It has already been suggested in previous references to bleaching that the desired results are obtained when the pulp and bleach are left in contact with one another in tanks or drainers until the bleach is completely exhausted, the residual salts in solution being removed by thorough washing. _Gelatine._--For animal-sized or tub-sized papers gelatine is used. It can be prepared by the paper-maker from hide clippings, sheep skins, bone, etc., or can be purchased ready made. Beadle gives the following interesting details as to the amount of gelatine which can be obtained from wet hide pieces:-- WEIGHT OF WET HIDE PIECES, 2,128 LBS.