362 METHODS OF ANALYSIS [Chap. 



Add 10 cc. of water to the residue, mix Vv^ell and transfer the mixture to a 

 small separatory funnel by means of a little water. Extract with 3 successive 

 portions of 10, 5 and 5 cc. of ether. Collect the ether extracts in a 50 cc. beaker 

 and designate this solution as B. 



(b) Dis'ntegrate 25 tablets in a small beaker with 10 cc. of water, breaking 

 up any lumps with a glass rod, and transfer by means of a little water to a sepa- 

 ratory funnel. Rinse the beaker with 10 cc. of ether and transfer this also to the 

 funnel. Shake thoroughly, draw off the aqueous layer and transfer the ether 

 through a funnel, containing a little cotton, to a 50 cc. graduated fiask. Repeat 

 the extraction with successive portions of ether until the flask is filled to the mark, 

 stopper and mix well. Designate this solution as C. 



In hand-made and soft compressed tablets, the method described under fa) is 

 preferred, since the direct extraction of the dry crushed material with ether re- 

 moves most of the nitroglycerin. In hard compressed tablets, the direct extraction 

 is often not nearly so complete and, in such cases, the method described under (b) 

 is to be preferred. 



Nitrate Method^. — Tentative. 



34 REAGENTS. 



(a) Phenoldisulphonic acid solution. — Prepare as directed under IV, 14 (a). 



(b) Standard nitrate solution.—Dissolve 0.7217 gram of potassium nitrate in 1 

 liter of water. Evaporate 10 cc. of this solution just to dryness in a porcelain dish 

 on a steam bath. Cool and treat the residue with 2 cc. of the phenoldisulphonic 

 acid solution, rubbing with a glass rod to insure intimate contact. After 5-10 min- 

 utes dilute to 250 cc. Each cc. of this solution contains 0.004 mg. of nitrogen. Add 

 an excess of potassiiun hydroxid solution to an aliquot of this solution and dilute 

 to 100 cc. (Do not use sodium or ammonium hydroxid.) It is advisable to pre- 

 l)are a standard of approximately the same color as the unknown. 



35 DETERMINATION. 



Place 20 cc. of the ether solution, A or C under 33, in a dried, tared 50 cc. beaker. 

 Evaporate the solvent in a vacuum desiccator containing sulphuric acid. Apply 

 the vacuum gradually, to prevent boiling. Allow the beaker to remain in the 

 vacuum 30 minutes after the ether has evaporated. Weigh and calculate the ether 

 extract per tablet. Treat the residue with 2 cc. of the phenoldisulphonic acid solu- 

 tion, rotating the beaker so that the reagent comes in contact with the entire inner 

 surface. After 10 minutes add water and wash into a 100 cc. flask. Dilute to the 

 mark and place 10 cc, representing 1 tablet, in a 100 cc. flask, add about 50 cc. of 

 water and a few drops more of 20% potassium hydroxid solution than is required to 

 neutralize the acid. Dilute to the mark and compare the color with that pro- 

 duced when a standard nitrate solution is similarly treated. Any convenient col- 

 orimeter or Nessler tubes may be used. Multiply the nitrate nitrogen found by 

 5.4 to obtain the equivalent of nitroglycerin. 



When 33 (a) is used for the p.eparat'on of the sample, a correction, deter- 

 mined as directed in 37, should be made for the amount of nitroglycerin in B 

 under 33, using all of B instead of an aliquot. 



Nitrite or Modified Hay Method^ .—Tentative. 



36 REAGENTS. 



(a) Sulphanilic acid solution. — Prepare as directed under IV, 12 (b). 



(b) Alpha-naphlhylamin hydrochlorid solution. — Prepare as directed under IV, 



12 (c). 



