UNI 



United States Department of Agriculture, 



BUREAU OF CHEMISTRY Circular No. 10 (Revised). 

 H. W. WILEY, Chiei ot Bureau. 



METHODS OF ANALYSIS OF INSECTICIDES AND FIX.K I DES. 



GENKHAL 



Samples of paris green, london purple, soft soap, copper carbonate and tobacco 



xtracts are to be thoroughly mixed before analysis, taking care that tin- first 



\\.. -amples an- not further pulveri/ed. Samples of lye and potassium cyanid 



are to be weighed in large quantities in weighing bottles and aliquot portions 



rom a \\ater solution taken for analysis. 



PAH is CK'KKN. 



Pi;n\ |SK>NAL).l 



Pry 1 to _ 10 liours at lo:> to IK) (', and calculate the loss as 



iK>i -hire. 



TOT.M ARSEHIODG <>\n>. Mi:moD I (OFFICIAL). 



SOLUTIONS REQUIKl l>. 



A Starch -olution is used \\hieh is prepared by boiling L' grams of starch with 

 200 cc of distilled water for about "> minutes. 



A .-tandard iodin solution is prepared in the following manner: Dissolve PJ.7 



;rams of p ( . \\dered iodin in about !'")( ) cc of water to which has been added is 



ams of C. P. potassium iodid, and make up the whole to a volume of 2 



-landardi/e this solution, weigh out 1 gram of C. P. dry arsenioiis 



>xid, tran-fer to a '_'~o-cc lla.sk by means of about lOOccof a solution containing 



mis of sodium hydroxid in each 100 cc, and boil until all arsenious oxid 



into solution. Make up to a volume of 250 cc and use^oO cc for analysis. 



Thi- ~'i < portion is concentrated, by boiling in a 250-cc flask to half its volume, 



and allowed to cool to about 80 C. An equal volume of concentrated hydro- 



id is now added, accompanied by .". grams of potassium iodid, mixed, 



and the \\ hole allowed to stand for 10 minutes (to reduce the arsenic oxid formed 



by boiling and the alkaline arsenite to arsenious oxid). The brown solution is 



then diluted \\jth cold water and an approximately tenth-normal solution of 



MM thiosnlphate added drop by drop, until the solution becomes exactly 



colorless. iThisend point is easy to read \\ithout the aid of starch.) This solu- 



tion is made slightly alkaline with dry sodium carbonate ( using a drop of methyl 



BJC to read the change) and then is made slightly acid with hydiochlorie 



ne that all lumps of sodium carbonate on the bottom are acted on 



by the hydrochloric acid. Sodium bicarbonate is now added in excess and the 



'on of iodin run in drop by drop, using starch water to read the end reaction. 



.-times the solution gets dark toward the end of the titration. This change 



must not be confused with the final dark blue "color given by the iodin and 



' i. i 



1 TV -ional" and "official" refer to adoption of methods by the Association of 



utural Clu-raists. 



