INSECTICIDES AND FUNGICIDES. 33 



varying from 400 to 500 cc. When the distillation is complete, only about 15 

 cc of the liquid should remain in the distillation flask. Titrate the distillate 

 with standard sulphuric acid, using phenacetolin or cochineal as Indicator. 

 One molecule of sulphuric acid is equivalent to two molecules of nicotln. 



9. Formaldehyde Solutions (Formalin, etc.). 

 (a) FORMALDEHYDE,* METHOD I (MODIFIED HYDROGEN PEROXID). PROVISIONAL. 



(1) SOLUTIONS REQUIRED. 



A normal solution of sulphuric acid, a normal solution of sodium hydroxid, 

 and a solution of purified litmus. 



(2) DETERMINATION. 



Measure out 50 cc of normal sodium hydroxid in a 500 cc Erlenmeyer flask 

 and add 50 cc of hydrogen dioxid. Then add 3 cc of the formaldehyde solution 

 under examination (the specific gravity of which has been previously deter- 

 mined), allowing the point of the pipette to almost reach the liquid in the flask. 

 Place a funnel in the neck of the flask and put on the steam bath for five min- 

 utes, shaking occasionally during this time. Remove from the steam bath, wash 

 the funnel with distilled water, cool the flask to about room temperature, and 

 titrate the excess of sodium hydroxid with normal acid, using litmus as indi- 

 cator. This cooling of the flask before titration with acid is necessary in order 

 to get a sharp end reading with the litmus. From the volume of formaldehyde 

 used and the specific gravity determine the per cent of formaldehyde. 



(b) FORMALDEHYDE,** METHOD II (CYANID). PROVISIONAL. 

 (To be used especially in solutions containing a small amount of formaldehyde.) 



(1) SOLUTIONS REQUIRED. 



(a) Silver nitrate. A tenth-normal solution. 



(&) Ammonium sulpho-cyanate. A tenth-normal solution. 



(c) Potassium cyanid. A solution containing 3.1 grams to 500 cc of water. 



(d) Nitric acid. A 50 per cent solution. 



(2) DETERMINATION. 



Treat 15 cc of the silver nitrate with 6 drops of 50 per cent nitric acid In 

 a 50 cc flask ; add 10 cc of the solution of potassium cyanid and shake well. 

 Then make the solution to the mark and titrate an aliquot of the filtrate (say 

 25 cc) according to the method of Volhard (page 23) with the tenth-normal 

 solution of ammonium sulpho-cyanate for the excess of silver. Acidify another 

 15 cc portion of tenth-normal silver nitrate with 6 drops of 50 per cent nitric 

 acid and treat with 10 cc of the potassium cyanid solution to which has been 

 added a weighed quantity of the dilute formaldehyde solution. Make up the 

 whole to 50 cc and titrate a 25 cc filtrate from it with tenth-normal ammonium 

 sulpho-cyanate for the excess of silver as before. The difference between these 

 results multiplied by 2 gives the amount of potassium cyanid that has been 

 used by the formaldehyde in terms of tenth-normal ammonium sulpho-cyanate. 

 Each cubic centimeter of this is equivalent to 3 milligrams of formaldehyde. 



Ber. d. chem. Ges., 1898, 81: 2979; J. Amer. Chem. Soc., 1905, 27: 1183. 

 6 Zts. anal. Chem., 1897, 36: 18. 



