There is a bleaching preparation made in France known as "Redo," which is simply calcium hydrosulphite (CaS2O4). This is used in the sugar industry to some extent, but it is claimed by many that the results obtained are not as good as those obtained from the sodium compound and that it deteriorates more easily. Hydrosulphites, unlike sulphurous acid, will bleach equally as well in alkaline or neutral medium, as in an acid medium. There is therefore less danger from loss of sugar by inversion when they are used, while the permanency of their effect is about the same. In any case where juices have been bleached by sulphites, the result may be considered as but temporary, since upon exposure to air and light the product assumes a darker color. Hydrosulphites should therefore be introduced as late in the process as possible. Where the material in the vacuum pan is to be bleached, it is well to introduce this reagent just before striking grain, thus furnishing a bright clear material which will act as film over the nucleous of sucrose in the grain. The chemical equation representing the change which takes place with this reagent is as follows: Na2S2O4 (sodium hydrosulphite) + O (oxygen) + H2O (water)-->2(Na H S O3). The amount to be used will depend absolutely upon individual conditions, which may be ascertained only by experimentation. The manufacturers of this product state that the amount of the material used to that of dry sugar should be as 1 is to 10,000. In the writer's experience, two or even three times this amount will usually be required to give maximum results. As stated before, since there is such a variance in the material to be treated, each operator will be required to judge this to a great extent from the condition of his product. In these Islands where a very low grade of open-kettle sugar is still made, which sells very cheaply, attempts are often made to bleach it and recrystalize in order to make a centrifugal sugar. While ordinary clarifying agents help to a great extent, if the melted sugars are very dark from caramel and the decomposition products of calcium glucosate, these reagents can not be expected to give a light-colored juice. While they may improve conditions somewhat, the only solution to such a problem is the use of the boneblack process. Bluing.--In the production of plantation clarified sugars, and sometimes of refinery crystals made from low-grade sugars, there is a thin film surrounding each sugar crystal, which has a yellowish tint. It is this that gives rise to the different grades of white sugars, when color test only is considered. Since this yellowish tinge will give way to a lighter color when neutralized with the proper shade of blue, it is a very common practice to use some form of bluing--usually that known as ultramarine--for this purpose.