10 



METHOD. 



Measure out 50 cc of normal sodium hydroxid in a small Erlenmevcr flask (of 

 500 cc capacity, for example) and add 50 cc of hydrogen dioxid. Now add 3 ccl 

 of the formaldehyde solution under examination (the specific gravity of which | 

 has been previously determined), 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 5 minutes, shaking occasionally during this time. Remove 

 from the steam bath, wash the funnel with distilled water, cool the flask down 

 to about room temperature, and titrate the excess of sodium hydroxid with 

 normal acid, using litmus as indicator. This cooling of the flask before titration 

 with acid was found necessary in order to get a sharp end reading with the 

 litmus. From the volume of formaldehyde used and the specific gravity the per 

 cent of formaldehyde can be determined. 



FORMALDEHYDE, METHOD II (PROVISIONAL). 



SOLUTIONS REQUIRED. 



A tenth-normal solution of silver nitrate, a tenth-normal solution of ammonium 

 sulpho-cyanate, a dilute solution of potassium cyanid containing 3.1 grams to 500 

 cc of water, and a 50 per cent solution of nitric acid. 



METHOD. 



Fifteen cubic centimeters of tenth-normal silver nitrate are treated with 6 drops 

 of 50 per cent nitric acid in a 50-cc flask ; 10 cc of a solution of potassium cyanid 

 (containing 3.1 grams of potassium cyanid in 500 cc of water) are then added 

 and well shaken. The solution is then made to the mark and an aliquot portion 

 of the filtrate (say 25 cc) is titrated according to the method of Volhard with a 

 tenth-normal solution of ammonium sulpho-cyanate for the excess of silver. 

 Another 15-cc portion of tenth-normal silver nitrate is acidified with (> drops of 

 50 per cent nitric acid and treated with 10 cc of the potassium cyanid solution 

 .to which has been added a weighed quantity of the dilute formaldehyde solution. 

 The whole is made up to 50 cc and a 25-cc filtrate from it is titrated with tenth- 

 normal ammonium sulpho-cyanate for the excess of silver as before. The differ- 

 ence 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. 



LIME-SULPHUR DIPS AND LIME-SULPHUR-SALT MIXTURE (PROVISIONAL). 



TOTAL SULPHUR. 

 SOLUTIONS REQUIRED. 



A saturated potassium hydroxid solution or a solution of caustic soda con- 

 taining 100 grams to 100 cc of water. A 10 per cent barium chlorid solution. 

 An approximately 3 per cent solution of hydrogen peroxid free from sulphates ; 

 if it contains sulphates add freshly precipitated barium carbonate and shake 

 occasionally for several hours, then filter and use the clear solution. 



METHOD. 



Measure off 10 cc of the clear sample in a 100-cc measuring flask and fill to 

 the mark. Use aliquot portions of 10 cc of this for analysis. Treat this aliquot 



1 Has been recommended once as an official method. 



