Practical organic and bio-chemistry / by R.H.A. Plimmer.

  • Robert Plimmer
Date:
1915
Catalogue details

Licence: Public Domain Mark

Credit: Practical organic and bio-chemistry / by R.H.A. Plimmer. Source: Wellcome Collection.

    567/660 page 547
    The evaporated solution is stirred with 20 c.c. of 95-96 per cent. alcohol ; after settling, the liquid is poured through a g cm. filter paper, which has been dried to constant weight at roo° in a stoppered weighing bottle (2 x 14 inches) or on a Gooch with a layer of asbestos } inch thick; the residue is treated with to c.c. Of 95 per cent. alcohol containing ‘2 per cent. of perchloric acid ;1! the insoluble potassium perchlorate is transferred to the filter, the last portions being washed upon it by means of 20-30 c.c. of the alcohol containing perchloric acid. The perchloric acid is washed away by a minimal quantity of alcohol as shown by testing the washings with sensitive litmus paper. It is important to wash the top edges of the filter paper thoroughly as it will blacken on the subsequent drying at 100°; as much as 120-150 c.c. of alcohol may be used. The paper is dried in the funnel at 100° for 20 minutes, and then in the weighing bottle until the weight is constant (r mgm. KC]O, = 0°3401 mgm. _K,0). As Cobaltinitrite. H. H. Green ” has adapted the cobaltinitrite method for estimating potas- sium in urine :— 25 c.c. of urine are evaporated to dryness in a platinum dish and gently ignited at a dull-red heat. The ash is moistened with nitric acid and reignited until it is free from organic matter and ammonium salts. The ash is dissolved in water containing a few drops of dilute hydrochloric acid and washed into a 200 c.c. porcelain basin. The solution is neutralised or made slightly alkaline with a few drops of caustic soda, acidified with acetic acid, and evaporated to between 5 and io c.c. 1 c.c. of glacial acetic acid and to c.c. of cobaltinitrite reagent? are added, and the evaporation continued until the syrup will set to a stiff mass on cooling. The cold mass consisting of the yellow precipitate, K,NaCO(NO,). . H,O, embedded in a dark-purple matrix, is stirred up and allowed to soak with 50 c.c. of 10 per cent. acetic acid until the precipitate is disentangled and the solution has a tawny colour. The yellow precipitate is washed by decantation with dilute acetic acid, the washings being poured through an asbestos filter. The precipitate is com- pletely transferred to the filter, washed with cold water, and sucked dry. Six washings by decantation with altogether 300 c.c. are generally sufficient. Complete retention of the precipitate may be attained by using a second disc of asbestos on the first. During the washing 300 c.c. of water are heated to boiling, and excess (30-50 c.c.) of ‘2N permanganate is added from a burette. The . asbestos and the precipitate are dropped into this solution and the remainder washed in. Sufficient sulphuric acid (20 c.c. of 25 per cent.) is added, the mixture well stirred, and gently boiled for about 5 minutes until the yellow pre- cipitate is completely decomposed. Manganese hydroxide separates out. Standard oxalic acid is run in from a burette until it has dissolved and the liquid is clear and of a very faint pink colour. The excess of oxalic acid is titrated with ‘2N permanganate. The difference between the amounts of oxalic acid and permanganate gives the amount of permanganate used. rt c.c. °2N KMnO, = o’00r714 gm. K,O. It is advisable to standardise the permanganate against potassium chloride ; a concentration of permanganate, so that 1 c.c.=0'’oo2 gm. K,O is more con- venient than exactly -2N. 31°6 c.c. of this strength of permanganate = 10 c.c. of 1 per cent. KCl. 1 Prepared by adding 5 c.c. of 20 per cent. perchloric acid to 500 c.c. of alcohol. 2 Biochem. J., 6. 8 This is prepared by dissolving 113 gm. of cobalt acetate in 400 c.c. of water and adding 100 ¢.c. glacial acetic acid ; 220 gm. of sodium nitrite are separately dissolved in 400 c.c. of water and the two solutions are mixed with stirring. The last portions of NO, are removed by evacuation or by blowing air through the solution. After 24 hours any sediment is filtered off and the volume diluted to 1 litre. The solution has a dark-plum colour, is kept in the dark and is decanted before use. se
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