THE ANALYST. 17 MONTHLY RECORD OF GENERAL RESEARCHES I N ANALYTICAL CHEMISTEY. ESTIMATION OF THE DECOLOURISING POWER OF AKIMAL CIIARCOAL. G. LAUBE. Repert. Anal. Chem., 1886, No. 49.-Analysts, unless engaged in sugar refineries, are not often called upon to perform this analysis, and therefore do not as a rule possess the required costly apparatus. The author therefore thinks an easy and practical process will be of some service to them. As a rule the questmion is merely whether a char has already been used or not. The first thing is to select a sample of undoubtedly genuine char, t o remove any whitish or suspicious-looking particles, then to powder and pass through a sieve. The powder is dried at 110" C., and kept in a stoppered bottle. It is labelled Standard Animal Charcoal.100 grammes of the commercial article, which has about the thickness of honey, are dissolved in 100 C.C. of water, then mixed with 100 C.C. of alcohol, and diluted with water up to one litre. After standing for a day or two, it must be filtered.. It is labelled Standard Colouring. The decolourizing power ( = 100) of the standard charcoal is now determined as follows :-Five grammes are put into a not too small flask, mixed with 300 C.C. of water, and heated to boiling. 10 C.C. of the standard colour are now added, and the whole again boiled for ten minutes, under an upright condenser, to avoid loss by evaporation, The fluid is now filtered through a double filter ; the filtrate, which must be quite clear, is, after cooling, mixed with a drop of solution of caustic soda, and put into a cylindrical glass. 200 C.C. of water, and a drop of caustic soda, are now put into another cylinder of exactly the same diameter, and as much standard colour is now added as will give it the same depth of colour aa the filtrate from the char. Suppose 2.1 C.C. were required, the char would have absorbed 10 - 2.1 = 7.9 C.C. standard colouring. If now a suspected sample should, when similarly treated, absorb 10 - 4.5 = 5.5 c.c standard colour, its decolourizing coefficient mould be- A solution of caramel is now prepared. 5.5 x 100 - 70. -- 7.9 As the decolourizing power also depends in a slight degree on tlie state of division, the same sieve must be used. L. DE R.