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The Estimation of Potassium, especially in Fertilisers, Soil Extracts and Plant Ashes

Published online by Cambridge University Press:  27 March 2009

William A. Davis
William A. Davis
Affiliation:
(Rothamsted Experimental Station)
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Extract

It is shown that whereas the platinum chloride method of estimation is uncertain and liable to give varying results, the perchlorate method described is at once more simple in manipulation and more uniform and exact in its results. An improvement has been introduced which consists in washing the perchlorate precipitate with 95% alcohol saturated with potassium perchlorate by means of which any error due to the solubility of the precipitate is obviated. This is of importance when dealing with small quantities of precipitate. The following other advantages may here be enumerated:

Type
Research Article
Information
The Journal of Agricultural Science , Volume 5 , Issue 1 , October 1912 , pp. 52 - 66
Copyright
Copyright © Cambridge University Press 1912

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References

page 55 note 1 An obvious method of avoiding this difficulty would of course be to use in washing 80% alcohol which has been previously saturated with pure potassium platinichloride.

page 57 note 1 This quantity is sufficient in most cases, but if the quantity of KCl + NaCl exceeds 0·2grm., 5 c.c. of perchloric acid or more should be used. It is necessary only to take about 1½ times the quantity of HCIO4 theoretically necessary to decompose all the salts present.

page 57 note 2 If the liquid evaporates to dryness no harm is done so long as there is no loss by spirting. It is only necessary to take up with a drop or two of the perchloric acid solution.

page 57 note 3 Made up by adding 5 c.c. 20% perchloric acid to 500 c.c. 95% alcohol.

page 65 note 1 As the solubility of the perchlorate in 95% alcohol somewhat rapidly increases with rise of temperature, it is necessary to saturate the alcohol with perchlorate at approximately the temperature of working. This can easily be done by keeping a Winchester quart full of alcohol in contact with the powdered perchlorate and filtering off fresh quantities just before use. Experience has shown that alcohol saturated on a cold day will dissolve 1 to 2 mgrm. per 50 c.c. when the temperature rises from 75° to 80° F.