Chimie des pâtes et papier . beunder-brûlés dans ce cas, elles peuvent faire preuve de beaucoup yellowflame même après qu'il est déchargé dans le lessivage des réservoirs. Underordinary conditions un 20 pieds fourneau exploité par experiencedmen va produire 30 à 33 tonnes de cendres dans vingt-quatre hoursand en vertu de conditions exceptionnellement favorables le produit maygo aussi haut que 42 à 43 tonnes. La doublure d'une telle fournaise willnot durer beaucoup plus de six mois et s'il est poussé plus dur qu'être itshould il wqt besoin de réparations plus tôt. La récupération des cendres dans la soude contient 65 à 80  % de carbonate de sodium Meech

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Chemistry of pulp and paper making . beunder-burned in which case it may show considerable yellowflame even after it is dumped into the leaching tanks. Underordinary conditions a 20-ft. furnace operated by experiencedmen will produce 30 to 33 tons of ash in twenty-four hoursand under exceptionally favorable conditions the product maygo as high as 42 to 43 tons. The lining of such a furnace willnot last much over six months and if it is pushed harder than itshould be it wiU need repairs rather sooner. The recovered ash in the soda process will contain 65 to 80per cent of sodium carbonate according to the care with whichit has been burned. There are small amounts of iron, alumina, lime, sulphur and silica derived from various sources and about18 to 22 per cent of carbon. From the furnaces the ash goes to some form of leachingdevice, either open tanks or closed tanks to which pressure canbe apphed. In the open tanks it is first flooded with weakliquor from below in order to avoid causing explosions when 134 THE SODA PROCESS. LOSSES 135 water comes in contact with the glowing ash. The washingis carried out systematically in order to produce a leach liquorof good strength and at the same time lose as little soda aspossible. The closed tank system saves floor space and timein leaching but much care is necessary in order to avoid explo-sions. There seems to be Httle to choose between the twosystems so far as operating efficiency is concerned. Black Ash Waste. This material, which remains in the leach-ing tanks at the end of the washing, consists of light porous car-bon contaminated with small amounts of impurities. Becauseof its physical condition it is very difficult to remove the waterit contains. When drained as much as possible in the leachtanks it still contains 80 to 85 per cent of water, even in the toplayers which are driest. The use of a centrifugal machine willnot reduce this moisture below 65 to 68 per cent and beyondthis point it can be dried only by the applica

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