APPENDIX 151 



Potash. — 50-100 C.C. of the solution are evaporated to dryness after 

 addition of 0-5 gram of pure CaCOj if the original soil did not effervesce 

 when HCl was added. Two courses are then open : — 



(a) The residue is gently ignited over a Bunsen burner till it is completely 

 charred, it is then taken up with water several times till all the potassium 

 chloride is dissolved (Neubauer's method ^ (212)). To the clear filtrate 5 c.c. 

 of platinum chloride (containing "005 gram Pt per c.c.) are added and the 

 mixture slowly concentrated on the water bath to a very small bulk. The 

 potassium platino-chloride is filtered off in a Gooch crucible, washed with 

 80 per cent, alcohol, dried and weighed. 



or {b) Add 10 c.c. of 5 per cent, baryta solution, evaporate to dryness, 

 ignite and take up with water as in (a), add 2-5 c.c. perchloric acid (sp. gr. i"i2), 

 concentrate till dense fumes are given off, allow to cool, add 20 c.c. 95 per cent, 

 alcohol and stir. Decant off the clear alcohol, add 40 c.c. alcohol containing 

 o'2 per cent, perchloric acid, transfer to a tared filter paper, wash with 50-100 

 c.c. of 95 per cent, alcohol till the runnings are no longer acid, dry at 100°, 

 and weigh as KCIO^. 



Phosphoric Acid. — The charred residue from which the potassium 

 chloride has been removed is now extracted with hot dilute H2SO4, the 

 filtrate is neutralised with ammonia, treated with 25 c.c. HNO3 ^^^ ^° 

 c.c. 0-9 sp. gr. ammonia. Warm to 55° C, add 35 c.c. ammonium 

 molybdate, allow to stand for a short time, filter. Wash with i per cent. 

 NaNOg till the washings are neutral, transfer the precipitate and filter paper 

 to the beaker used for the precipitation, and add a known volume of standard 

 alkali so that the precipitate completely dissolves. Measure the excess by 

 titration, using phenolphthalein as indicator. If 3237 c.c. of normal acid 

 or alkali be diluted to i litre then i c.c. = -ooi gram PjO,.^ 



Available Potash and Phosphoric Acid. — Dyer's directions are as follows : 

 200 grams dry soil are placed in a Winchester quart bottle with 2 litres of dis- 

 tilled water in which are dissolved 20 grams of pure citric acid. The soil is 

 allowed to remain in contact with the solution at ordinary temperatures for 

 seven days, and is shaken a number of times each day. The solution is then 

 filtered, and 500 c.c. taken for each determination ; this is evaporated to dry- 

 ness, and gently incinerated at a low temperature. The residue is dissolved 

 in hydrochloric acid, evaporated to dryness, redissolved, and filtered ; in the 

 filtrate the potash is determined. For the phosphoric acid determination the 

 last solution is made, as before, with nitric acid. 



Mechanical Analysis. — 'The object is to obtain information about the size 

 of the ultimate particles of which the soil is composed ; the compound par- 

 ticles are therefore broken down by treatment with hydrochloric acid, and 

 after with ammonia. Direct measurement of the ultimate particles is found 

 to be impracticable ; indirect methods have to be adopted, depending on the 

 > The older method due to Tattock is still sometimes used. It is described by Dyer 



^ This volumetric method is described in Bull, 46 (revised) United States Division of 

 Chemistry (Washington, 1898). The older method is described by Dyer (91). 



