Potato starch is largely bleached by the application of sulphuric acid, this being absolutely requisite when the potatoes are at all decayed. After the use of the sulphuric acid, any remaining traces of acid must be neu-tralized by ammonia or milk of lime, fixed caustic alkalies being inadmissible. Chlorine is also much used for bleaching starch, usually as a solution of calcium chloride in water soured by the addition of sulphuric acid; this and some other salts cause the grains to swell, and render them soluble in cold water. Sal ammoniac is another favourite agent. - (Spons' 'Encyclopaedia.')