646 AGRICULTURAL ANALYSIS 



the solution is acid. Then add ammonia in slight excess and 

 filter if a precipitate appears. Determine the lime in the filtrate 

 by precipitating with ammonium oxalate and finally weighing as 

 calcium oxid. 



540. Kerosene Emulsion. In kerosene emulsions as usually pre- 

 pared the emulsifying agent is soap. On account of the trouble 

 of preparing these mixtures at home, various kerosene emulsions 

 in a concentrated form have appeared upon the market in late 

 years. In determining the value of an emulsion of this kind it 

 is usually only necessary to determine the amount of kerosene 

 present. A centrifugal method has been worked out by Colby 

 which seems to give very excellent results. 20 



Kerosene. Weigh six, nine, or even 18 grams according to 

 the strength of the kerosene emulsion, and measure in cubic 

 centimeters at 15.5 into a babcock cream bottle, graduated 

 to 35 or 50 per cent. To this add three or four cubic 

 centimeters of strong sulfuric acid and twirl one minute 

 in a babcock machine; then add cold water and twirl again one 

 minute ; finally add water sufficiently to bring the water to or 

 above the zero mark in the neck of the babcock bottle ; read the 

 cubic centimeters of kerosene at 15.5. Calculate the volume 

 percentage of kerosene on the number of cubic centimeters of 

 emulsion used in the test. 



541. Tobacco and Tobacco Extract. Decoctions of tobacco and 

 diluted tobacco extracts are often used against external sucking 

 insects. They are valued by the entomologist for the amount of 

 nicotin which they contain, hence this is the only determina- 

 tion necessary in analyses of such articles. The Association of 

 Official Agricultural Chemists has made careful studies of the 

 Lloyd and Winton methods of determining nicotin, but unsatis- 

 factory results were obtained. 27 The only method that has given 

 satisfactory results, is that of Kissling. The Emery method, 

 tested by the association in 1904, appeared to lead to fairly sat- 

 isfactory results. 



28 Bureau of Chemistry, Bulletin 105, 1907 : 165. 



17 Bureau of Chemistry, Bulletin 56, 1899 : 114, 125 ; Bulletin 73, 1903 : 

 165; Bulletin 81, 1904 : 203. 



