By D. W. Gilchrist Shirlaw and J. E. Nichols (Auth.)
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THE DETERMINATION OF CARBONATE BY COLLINS' CALCIMETER A more elaborate apparatus, which eliminates the requirement for standardization and, in consequence, is more speedy where a number of samples are to be analysed, is Collins' calcimeter. This is illustrated in Fig. 4. It consists of a 150 ml conical flask (A) into which the soil is weighed; the hydrochloric acid (30 per cent) is placed in a graduated cylinder (B) which is in turn placed in the flask. The flask is connected by pressure tubing to the top of a 50-ml graduated tube (C); into this rubber connection is inserted a " T " tube (D) with a stopcock (E) in the limb open to the atmosphere.
Approximately 25 g of soil (less for a calcareous soil) are weighed out and placed in a 500-ml conical flask. 2. 25 ml of N / 1 0 hydrochloric acid are pipetted into a flask and the flask well shaken. 3. T h e reaction is allowed to continue to completion; up to 1 hr may be required for this stage. 4. 25 ml of distilled water are now added and the flask again shaken. 5. T h e suspension is now filtered; double filtering may be necessary to obtain a sufficiently clear solution, if required, the solution can be cleared by shaking with activated charcoal between filterings.
This should take no less than 4 hr and preferably no longer than overnight. T h e speed of leaching will depend in part on the compaction of the glass wool and of the soil. If preferred a short length of rubber tubing and a screw clip can be fixed on to the bottom of the funnel to gain better control of the flow rate. 8. When leaching is complete the bottom volumetric flask is removed and made u p to the mark with normal ammonium acetate. T H E ANALYSIS O F S O I L S 59 This solution is used for the determination of individual cations: Potassium is determined by flame photometry in a similar manner to that described under available nutrients (see sect.