Ammonium sulphate predpitation

Discussion. Some of the details of this method have already been given in Section 11.11(C), This procedure separates aluminium from beryllium, the alkaline earths, magnesium, and phosphate. For the gravimetric determination a 2 per cent or 5 per cent solution of oxine in 2M acetic add may be used 1 mL of the latter solution is suffident to predpitate 3 mg of aluminium. For practice in this determination, use about 0.40 g, accurately weighed, of aluminium ammonium sulphate. Dissolve it in 100 mL of water, heat to 70-80 °C, add the appropriate volume of the oxine reagent, and (if a precipitate has not already formed) slowly introduce 2M ammonium acetate solution until a precipitate just appears, heat to boiling, and then add 25 mL of 2M ammonium acetate solution dropwise and with constant stirring (to ensure complete predpitation). 

For a unit of digestive rennet in powdered form, we find 27 times more coagulating enzyme than in the same unit of pepsin In addition, we can, by suitable predpitations, increase one of the two powers to the detriment of the other, in other words, we can roughly obtain a separation of these two enzymes Thus ammonium sulphate, added to the saturation point to a solution containing the two enzymes, precipitates both, while sodium chloride similarly precipitates almost exclusively the rennet and leaves the pepsin in the solution. By repeating several times this predpitation with sodium chloride we can progressively enrich the predpitate in rennet. 

In test No. 1, the liquid is composed of 2 c.c. of peptone, 7 C.C. of water and i c.c. of saturated ammonium sulphate. The column precipitation indicates whether the mixture remains dear. Predpitation begins only in No. 3, and, consequently, the first lower limit corresponds to 2.6 c.c. of sulphate. Predpitation caused in No. 3 by the sulphate is far from being complete. The column Addition t6 filtered liquid indicates whether or not the liquid to which had been added 2.6 c.c. of sulphate, and then had been freed of predpitate by filtration, gives a new predpitate with 0.2 c.c. of sulphate. In No. 6,... 

Discussion. This method is based upon the precipitation of lead chlorofluoride, in which the chlorine is determined by Volhard s method, and from this result the fluorine content can be calculated. The advantages of the method are, the precipitate is granular, settles readily, and is easily filtered the factor for conversion to fluorine is low the procedure is carried out at pH 3.6-5.6, so that substances which might be co-predpitated, such as phosphates, sulphates, chromates, and carbonates, do not interfere. Aluminium must be entirely absent, since even very small quantities cause low results a similar effect is produced by boron ( >0.05 g), ammonium (>0.5 g), and sodium or potassium ( > 10g) in the presence of about 0.1 g of fluoride. Iron must be removed, but zinc is without effect. Silica does not vitiate the method, but causes difficulties in filtration. 

Solutions of cerium(IV) sulphate may be prepared by dissolving cerium(IV) sulphate or the more soluble ammonium cerium(IV) sulphate in dilute (0.5-1.0M) sulphuric add. Ammonium cerium(IV) nitrate may be purchased of analytical grade, and a solution of this in 1M sulphuric add may be used for many of the purposes for which cerium(IV) solutions are employed, but in some cases the presence of nitrate ion is undesirable. The nitrate ion may be removed by evaporating the solid reagent which concentrated sulphuric add, or alternatively a solution of the nitrate may be predpitated with aqueous ammonia and the resulting cerium(IV) hydroxide filtered off and dissolved in sulphuric acid. 

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