402 REAGENTS 



Phloroglucin. Prepare a saturated solution in alcohol. Treat 

 material with this for a short time, and then mount in strong 

 hydrochloric acid. 



Scharlack Red. Prepare a saturated solution in a mixture of 

 70 parts absolute alcohol and 30 parts water by volume. 

 Filter and keep well stoppered. 



Sulphuric Acid. For cellulose tests it is usual to employ the 

 concentrated acid. Great care must be exercised in its use, and 

 strong ammonia should be at hand to neutralise any drops that 

 may be spilled. 



III. Artificial Sea-water. For this purpose Tidman's sea-salt, 

 dissolved in distilled water in appropriate concentrations, can 

 be employed ; or a solution can be made according to the following 

 formula given by Osterhout : 



1,000 parts sodium chloride (gram-molecular solution). 

 78 ,, magnesium chloride (gram-molecular solution). 

 38 ,, magnesium sulphate (gram-molecular solution). 

 22 ,, potassium chloride (gram-molecular solution). 

 10 ,, calcium chloride (gram-molecular solution). 



This solution has an osmotic pressure of about 22*4 atmo- 

 spheres ; when diluted with an equal volume of distilled water, 

 the osmotic pressure is halved, when diluted with twice its 

 bulk of distilled water the osmotic pressure is one-third of that 

 of the undiluted solution, and so on. 



IV. Artificial Semipermeable Membranes. For this purpose 

 the membranous precipitate of copper ferrocyanide, formed when 

 solutions of copper sulphate and potassium ferrocyanide meet, 

 is often employed. The precipitate is customarily deposited 

 in the wall of a small pot of unglazed porous porcelain, which 

 is thoroughly washed so that it is impregnated with water. 

 It is then nearly filled with a dilute solution of copper sulphate 

 (2-5 grams per litre) and stood in a solution of potassium ferro- 

 cyanide (2-1 grams per litre), where it is left for some time. 

 Ultimately it is thoroughly washed and soaked in water. It is 

 best to prepare several pots in this way, as some are sure to be 

 faulty. To overcome this difficulty, Philip recommends depositing 

 the copper ferrocyanide precipitate in a film of gelatine, formed 



