188 PROTEINS AND CARBOIHYDRATES 
heat the closed end very gently at first and later heat the bottom to 
a dull red. As soon as the sodium has begun to volatilize and condense 
on the sides of the tube, add a few drops of the sample or a few pieces of 
a, solid, being careful to keep off the sides of the tube. As soon as the 
tube has cooled any excess of sodium may be removed by adding a little 
alcohol or if the sodium excess is not large the tube may be plunged into 
warm water. This solution must be filtered free of free carbon. The 
filtrate may then be tested for the halogens, nitrogen and sulphur. 
Hydrogen and oxygen are assumed to be present. 
Test for Organic Sulphur. Treat about 1 c.c. of the solution secured 
from the sodium ignition with lead acetate solution. If sulphur 1s 
present a black precipitate will be formed according to the following 
equation. The solution must be strongly alkaline. 
Nae2S-+ Pb(C2H302)2= PbS +2NaCoH30e. 
Sodium nitro-prusside may also be used to test for organic sulphur. 
Add a few drops to about 1 ¢.c. of the filtrate secured from the sodium 
ignition and if a violet color results, the presence of sulphur is indicated. 
Test for Organic Nitrogen. Add to about 3 c.c. of the filtrate four 
drops of NaOH solution, four drops of FeSOz solution and one drop of 
FeCl3. Add a little concentrated HCl to dissolve the precipitated 
ferrous and ferric hydroxides and boil. If N is present in the sample a 
precipitate of Prussian blue will come down. It may be necessary to 
heat the tube gently and leave it for a time. The following reactions 
take place: 
6NaCN+FeSO4 = NasFe(CN) 6+ NaeSOa, 
FeCls+NaOH =Fe(OH)3+3NaCl. 
4¥e(OH)3+3NasaFe(CN)¢+12HCl = Fes(Fe(CN) 6)3-+ 12H20+ 12NaCl. 
Test for Sulphur and Nitrogen when Present Together. Acidify 
about 1 ¢.c. of the solution with HCl and add three drops of ferric chloride 
solution. A dark red indicates the presence of sulphur and nitrogen. 
3NaSCN+FeCls = Fe(SCN)3+3NaCl. 
To be certain of results the above tests for sulphur and nitrogen should 
be made along with this test. 
Test for Organic Halogens: Group Test. This is carried out by 
removing HS, and cyanide. To do this the solution is acidified with 
dilute nitric acid and boiling. The addition of silver nitrate at this 
