1917] AGRICULTUBAL CHEMISTRY AGEOTECHNY. 505 



case the residue is not easily burnt white, it is best to dissolve in water and a 

 little hydrochloric acid and filter out insoluble matter. In many cases organic 

 matter and ammonium salts may be conveniently removed by evaporation of the 

 solution with aqua regia." After ignition the residual salts are best dissolved 

 by adding a few drops of hydrochloric acid and heating before adding much 

 water. 



" Separation of K:PtCle requires certain conditions for an accurate result. 

 Concentration of potassium at time of adding plat-inum must be low enough so 

 that no K;PtCU is precipitated at once. Free sulphuric acid, nitric acid, or 

 organic matter must not be present. The amount of platinum used should be 

 only slightly in excess of that necessary to combine with all the potassium. 

 Excess of hydrochloric acid is unimportant. Evaporation should cease while 

 some free hydrochloric acid still remains ; if evaporation is carried too far dilute 

 hj'drochloric acid should be added and the evaporation repeated." 



Five or six successive washings with 10 cc. of the wash fluids were found to 

 be sufficient. In the presence of large amounts of sodium, potassium is better 

 separated as cobaltinitrite than as platinichlorid. An ordinary Gooch crucible 

 with asbestos felt was found to be most suitable and reliable for accurate work 

 in collecting and purifying the precipitate. Drying can be accomplished at any 

 temperature between 100 and 140° C, and is usually complete in an hour at 

 120°. The final weighing should not be made in less than half an hour after 

 the removal from the oven. 



The perchlorate procedure for the determination of potassium was found to be 

 less reliable than the platinum method, and to be longer, more difficult, and 

 more expensive in regard to the reagents. 



A list of 30 references to the literature is cited. 



The action of solutions of ammonium sulphate on muscovite, R. F. Gak- 

 DiKER and E. C. Shorey {Jour. Indus, and Engin. Chem., 9 {1911), No. 6, pp. 

 589, 590 ) . — Analytical data relative to the extraction of potassium from musco- 

 vite by ammonium sulphate are submitted and briefly discussed. 



The influence of calcite inclusions on the determination of org'anic carbon 

 in soils, E. C. Shorey and W. H. Fey {Jour. Indus, and Engin. Chem., 9 {1911), 

 No. 6, pp. 588, 589). — The authors report the presence of calcite inclusi(,'us in 

 quartz of soils derived from limestones, as previously noted by McCaughey 

 and Fry (E. S. R., 28, p. 812) and by Robinson (E. S. R., 31, p. 719). The 

 effect of these inclusions on the determinations of the total carbon in such soils 

 by the cupric oxid combustion method is indicated by the analytical data sub- 

 mitted. The inclusions were found to introduce no error when the carbon 

 was determined by the wet oxidation method. 



The subject is briefly discussed. 



A new method for the determination of silicic acid (zeolitic) in soils, K. K. 

 Gedroits (C. GuEDROiTz) {Zliur. Opytn. Agron. {Jour. Agr. Expt.), 11 {1916), 

 No. 5, pp. 400-401). — The value of silicic acid determinations in studying the 

 transformations and origin of soils is indicated, and the disadvantages of the 

 procedures commonly used are noted. The following procedure is described 

 and deemed to yield excellent results : 



Five gm. of the sample is treated with 10 per cent hydrochloric acid and 

 heated in a small platinum crucible over a spread burner to a temperature not 

 higher than 625° C. After cooling, the mass is transferred with a little water 

 to a beaker, and 100 cc. of 5 per cent potassium hydroxid added. The material 

 is heated on the water bath for one-half hour, filtered, and washed with 1 

 per cent potassium hydroxid. The filtrate is acidulated with hydrochloric 

 acid, evaporated, and heated on a sand bath for from one to one and one-half 

 16179°— 17— No. 6 2 



