Vn] INSECTICIDES AND FUNGICIDES 73 



5g CHLORIN.K— OFFICIAL. 



After completion of the titration for cyanogen, as directed under 55, add a few 

 cc. of 10% potassium chromate solution as indicator and titrate with N/20 silver 

 nitrate until the appearance of the red-brown color of silver chromate. 



The first titration with silver nitrate represents the cyanogen present according 

 to the equation above. The second titration represents the cyanogen and chlorin 

 according to the following equation : NaCNAgCN + NaCl + 2AgN03 = 2NaN03 + 

 2AgCN + AgCl. Therefore the second minus the first reading represents the chlorin 

 present in terms of silver nitrate. 



SOAP. 



57 Modified Method of Benedickt and Lewkowitsch.^^ — Tentative. 



Weigh about 5 grams of the sample in a tared, 100 cc. beaker, in which is pre- 

 viously placed a 5 inch layer of recently ignited, dry sand, and a small glass rod; 

 if the soap is hard, cut off the soap in very thin strips. Add 25 cc. of alcohol, 

 or more if necessary, and dissolve on the water bath, stirring constantly. Evapo- 

 rate the alcohol, heat in an oven at 110°C. until the soap is nearly dry, and weigh, 

 then dry again for 30 minutes and weigh. Continue this alternate drying and 

 weighing until the weight changes only a few milligrams during the course of 30 

 minutes' drying. 



58 POTASSIUM AND SODIUM."— TENTATIVE. 



Dissolve about 5 grams of the soap in water; decompose with hydrochloric acid, 

 filter off the water and wash the fat with cold water. Determine both potassium 

 and sodium in the filtrate as directed under II, 21 . 



SODA LYE. 



59 CARBONATE AND HYDROXID.i'— OFFICIAL. 



Weigh about 10 grams of the sample from the weighing bottle, dissolve in car- 

 bon dioxid-free water and make up to a definite volume. Titrate an aliquot of this 

 solution with N/2 hydrochloric acid, using methyl orange as an indicator, and note 

 the total alkalinity thus found. Transfer an equal aliquot to a graduated flask 

 and add enough barium chlorid solution to precipitate all the carbonate, avoiding 

 any unnecessary excess. Dilute to the mark with carbon dio.xid-free water, stopper, 

 shake, and set aside. When the liquid becomes clear, pipette off one half and ti- 

 trate with N/2 hydrochloric acid, using phenolphthalein as an indicator. The 

 number of cc. of N/2 acid, required for this titration, multiplied by 2 gives the num- 

 ber of cc. of N/2 acid required to neutralize the sodium hydroxid present in the 

 original aliquot. The difference between this figure and the number of cc. of N/2 

 hydrochloric acid required for the total akalinitj' represents the number of cc. of 

 N/2 acid required to neutralize the sodium carbonate present in the aliquot. Cal- 

 culate the percentages of sodium carbonate and hydroxid present in the sample. 



TOBACCO AND TOBACCO EXTRACT. 



NICOTIN. 



Kissling Method. — Official. 



60 REAGENTS. 



(a) Alcoholic sodium hydroxid solution. — Dissolve 6 grams of sodium hydroxid 

 in 40 cc. of water and 60 cc. of 90% alcohol. 



