the filtrate with ammonia and ammonium carbonate, filter, evap- 

 orate the filtrate to dryness in a porcelain dish, and drive off the 

 ammonia salts by heat below redness. 88 When cold, re-dissolve in 

 15 or 20 cubic centimeters of water, precipitate again with a few' 

 drops of ammonia and ammonium carbonate solution, let stand a 

 few minutes on the water bath and filter into a tared platinum 

 dish and evaporate to dryness, expel the ammonia salts by heat- 

 ing to just preceptible dull redness, weigh the potassium and so- 

 dium chlorids obtained and determine the potassium chlorid with 

 platinic chlorid as usual. 



The potassium may also be determined by the perchlorate meth- 

 od, or the total chlorin be determined volumetrically, and the 

 relative percentages of potassium and sodium chlorids calculated 

 by the usual formula : Or multiply the weight of chlorin in the 

 mixture by 2.1035, deduct from the product the total weight of 

 the chlorids and multiply the remainder by 3.6358. The product 

 expresses the weight of the sodium chlorid contained in the mixed 

 salts. The indirect method is only applicable when there are con- 

 siderable quantities of alkalies present and where they exist in 

 approximately molecular proportions. It is, therefore, a process 

 rarely to be recommended in ash analysis. 



522. Latest Official Methods for the Determination of Inor- 

 ganic Plant Constituents. 89 i. Preparation of Sample. The ma- 

 terial must be thoroughly cleaned from all foreign matter, es- 

 pecially from adhering soil. It is to be ground and preserved in 

 carefully stoppered bottles. 



2. Determination of Carbon-Free Ash. (a) Preparation of 

 calcium acetate. Dissolve 20 grams of pure calcium carbonate 

 in pure acetic acid, and dilute to one liter. Evaporate 20 cubic 

 centimeters of the solution in a platinum dish, ignite gently, then 

 strongly, to constant weight. The dish must be weighed quickly. 

 This gives the calcium oxid in 20 cubic centimeters. 



(a') Alternative Method. Dissolve marble in hydrochloric 

 acid, evaporate, and dry to render silica insoluble, dissolve with 

 water and a little acid, and precipitate iron and aluminum in the 



88 Division of Chemistry, Bulletin 43, 1894 : 391. 



89 Bureau of Chemistry, Bulletin 107, 1907 : 21. 



