560 AGRICULTURAL ANALYSIS 



The first may be changed into platinic chlorid by fuming hydro- 

 chloric acid and a little nitric acid. The nitrous compounds may 

 be removed by the alternate addition of hydrochloric acid and 

 water during evaporation. It has further to be noted, that by 

 making use of platinum scrap from the laboratory, iridium com- 

 pounds may be present. These may be removed by precipitation 

 with ammonium chlorid and subsequent reduction. 



The purity of the platinic chlorid may be best proved by con- 

 ducting an analysis of potassium chlorid formed from pure mate- 

 rials of known composition. 



2. Perchloric Acid. An acid of 1.125 specific gravity should 

 be used and preparations of this strength are now offered to the 

 trade. 



3. The Barium Chlorid Solution. One hundred and twenty- 

 two grams of the crystallized salt with 50 cubic centimeters of 

 concentrated hydrochloric acid are dissolved in water, and made 

 up to one liter. 



4. The Calcium Saccharate Solution. Four hundred and fifty 

 grams of quicklime and 450 grams of sugar are dissolved in 

 seven liters of water. After shaking thoroughly for half an 

 hour the resulting precipitate is left over from two to three weeks. 

 The solution is then filtered and a further 450 gram of sugar 

 is added. The solution should preferably be stored and drawn 

 off in a closed bottle with a burette attachment. 



5. Alcohol. For washing the potassium chloroplatinate pre- 

 cipitates, alcohol of at least 96 per cent, purity should be employed. 



6. Filters. The most serviceable filter for the platinic chlorid 

 estimation of potash is the Swedish filter, Murktell I F. Many 

 otherwise excellent filter papers show a gain in weight after treat- 

 ing with 96 per cent, alcohol and drying at 120. This may 

 amount to several milligrams for a nine centimeter filter. On 

 this account it is advisable in taring a filter to omit moistening it 

 with alcohol before placing in the drying oven. 



473. Lunge's Modification of Technical Methods. The tech- 

 nical methods for the determination of potash in the Stass- 

 furt salts, which have just been described, are of great interest 

 to agricultural chemists in all parts of the world since, practical- 



