----------+-------------+-----------+----------------------- | | | Equivalent Percentage Specific | Degrees | Per cent. | of 60 per cent. Gravity. |Twaddle.[10] | Na_{2}O. | Caustic Soda. ----------+-------------+-----------+----------------------- 1·0040 | 0·80 | 0·302 | 0·503 1·0081 | 1·62 | 0·601 | 1·001 1·0163 | 3·26 | 1·209 | 2·015 1·0246 | 4·92 | 1·813 | 3·021 1·0330 | 6·60 | 2·418 | 4·030 1·0414 | 8·28 | 3·022 | 5·037 1·0500 | 10·00 | 3·626 | 6·043 1·0587 | 11·74 | 4·231 | 7·051 1·0675 | 13·50 | 4·835 | 8·059 1·0764 | 15·28 | 5·440 | 9·067 1·0855 | 17·10 | 6·044 | 10·073 1·0948 | 18·96 | 6·648 | 11·080 1·1042 | 20·84 | 7·253 | 12·090 1·1137 | 22·74 | 7·857 | 13·095 1·1233 | 24·66 | 8·462 | 14·103 1·1330 | 26·60 | 9·066 | 15·110 1·1428 | 28·56 | 9·670 | 16·117 1·1528 | 30·56 | 10·275 | 17·125 1·1630 | 32·60 | 10·879 | 18·131 1·1734 | 34·68 | 11·484 | 19·140 1·1841 | 36·82 | 12·088 | 20·147 1·1948 | 38·96 | 12·692 | 21·153 1·2058 | 41·16 | 13·297 | 22·161 1·2178 | 43·56 | 13·901 | 23·170 1·2280 | 45·60 | 14·506 | 24·177 1·2392 | 47·84 | 15·110 | 25·170 ----------+-------------+-----------+----------------------- NOTE.—It must be borne in mind that the above numbers refer only to solutions of pure caustic soda. With liquors containing sodium chloride, sulphate, &c., the specific gravity will give an erroneous view of the amount of alkali present, as these salts of course raise the gravity. For example, a liquor prepared by causticising a solution of recovered soda has a specific gravity of 1·05 (10° Tw.). According to the above table this corresponds to 6·043 per cent. of 60 per cent. caustic. Tested by means of standard acid it showed 4·520 per cent. Too much reliance should therefore not be placed upon determinations of specific gravity, but in important cases the actual amount of alkali should be determined by titration with standard acid. [Footnote 10: To convert degrees Twaddle into specific gravity, multiply by 5, add 1000 and divide by 1000: thus 7° Tw., 7 × 5 = 35 1000 ──── 1000) 1035 (1·035 sp. gr. 1000 ──── 3500 3000 ──── 5000 5000 ━━━━] {110} CHAPTER VII. BLEACHING.