This calcium hydroxide is a substance which is very caustic, and care must be exercised in handling it. Like all bases, it has a great affinity for acid, and consequently its first action is to neutralize part of the acids present. It then coagulates albumins and albuminoids, which form a part of the impurities, and throws down insoluble salts of sulphates, carbonates and phosphates, and of the bases iron and aluminum. These act as mechanical precipitants, assisting in bringing down other impurities. The compounds of calcium are practically insoluble in cold cane juices, and may be readily filtered, or settled, and the supernatant liquor drawn off. In the addition of lime, as well as in the application of other reagents, much care must be observed that the proper amount is added. If too little is used, there will be poor clarification and settling of the precipitate, while if too much is used, so that alkalinity is reached, and the juice heated to a high temperature, there will be a darkening of the juice caused by the decomposition of the reducing sugars by the calcium, and the formation of dark-colored compounds, which are very hard to remove. If the juice is limed to three-tenths or four-tenths cubic centimeter acidity against N/10 NaOH, using phenolphthalein as an indicator, there will be little or no chance of trouble. With the above dangers in view, it is not safe to employ the haphazard methods of liming usually practiced here, but the milk of lime should always be made of stated density and a measured or weighed amount should be supplied to each clarifier of juice, corresponding to prevailing conditions. Sulphur dioxide.--Where a better grade of sugar than 96° test is desired, it is often advisable to subject the juice to further treatment, one reason for which is to increase the acidity so that a larger amount of lime may be added to effect the clarification. In addition to this the sulphur acts to some extent directly as a clarifying agent, by precipitating some of the impurities. It also acts as a bleaching agent by extracting the oxygen from the impurities and lastly it acts as a disinfectant. It is formed by burning crude sulphur in a stove made for that purpose. S (sulphur) + O (oxygen heat)-->SO2 (sulphur dioxide). Sometimes bombs filled with liquid sulphur dioxide are purchased for this purpose. These are inconvenient to use, and this method is ordinarily more expensive than the usual one of burning the sulphur and producing the gas directly at the factory. Sulphur dioxide is a heavy gas which is very readily absorbed in water, and at a temperature of zero C. nearly 80 per cent by volume of the gas will be taken up. At 40° C. only about 18 per cent by volume of the gas will be absorbed. It may readily be seen that the percentage of gas contained in the juice when saturated will be determined by the temperature. The following equation expresses the absorption of sulphur dioxide in water at ordinary temperature: