I40 SOIL BACTERIOLOGY 



freshly prepared solution should be used. Proteins when 

 heated with Millon's reagent turn a brick red. 



Biuret Reaction. — ^Add sodium or potassium hydroxid 

 to a dilute sulphuric acid solution containing protein until 

 alkaline, and a few drops of a very dilute solution of copper 

 sulphate. The presence of protein will be marked by the 

 gradual spreading of a reddish-violet color through the 

 solution. 



Mercuric Chlorid. — ^A stock solution is prepared and 

 diluted to the desired strength. 



Stock Solution: Add i part of mercuric chlorid to 2.5 

 parts of commercial hydrochloric acid (40 per cent. HgCl2 

 inHCl). 



In order to prepare ax : xooo solution, the concentration 

 commonly used for disinfecting purposes, take 2.5 c.c. of 

 the stock solution and dilute to 1000 c.c. 



Solution for Sealing Bottles.— Melt together equal parts 

 of gutta-percha and paraffin. 



Seal for Museum Jars.— A transparent seal for museum 

 jars may be made by wetting celluloid with acetone. Cut 

 strips or rings of celluloid a little wider than the ground- 

 glass surface, dip in acetone, and place upon the edge of 

 the jar. Cover before the acetone evaporates and press 

 slightly. 



Preserving Plants in Natural Colors.— Saturate with 

 copper acetate a 50 per cent, glacial acetic acid solution in 

 water. 



Take 4 parts of water to i part of the stock solution. 

 Boil the plant tissue to be preserved for five to ten minutes, 

 or until the color becomes yellowish and then green. Wash 

 in water and preserve in a 4 or 5 per cent, solution of 

 formalin. 



