356 PHYSIOLOGICAL CHEMISTRY 



Formalin. (Neutral.) 



Dilute formalin 1-4 with distilled water, add a small 

 amount of phenolphthalein, and then add dilute (N/10) sodium 

 hydrate until the liquid acquires a faint pink tinge. 



Glyoxylic Acid Solution. 



Hopkins-Cole Reagent (Benedict's Modification). Ten 

 grams of powdered magnesium are placed in a large Erlen- 

 meyer flask and shaken up with enough distilled water to 

 liberally cover the magnesium. Two hundred and fifty cubic 

 centimeters of a cold, saturated solution of oxalic acid is 

 now added slowly. The reaction proceeds very rapidly and 

 with the liberation of much heat, so that the flask should be 

 cooled under running water during the addition of the acid. 

 The contents of the flask are shaken after the addition of 

 the last portion of the acid and then poured upon a filter, 

 to remove the insoluble magnesium oxalate. A little wash 

 water is poured through the filter, the filtrate acidified with 

 acetic acid to prevent the partial precipitation of the mag- 

 nesium on long standing, and made- up to a liter with dis- 

 tilled water. This solution contains only the magnesium salt 

 of glyoxylic acid. 



Guenzberg's Reagent. 



Dissolve 2 grams of phlorglucinol and 1 gram of vanillin 

 in 100 c.c. of 95% alcohol. 



Magnesia Mixture. 



Dissolve 175 grams of magnesium sulphate and 350 grams 

 of ammonium chloride in 1,400 c.c. of distilled water. Add 

 700 grams of concentrated ammonium hydroxide, mix thor- 

 oughly, and preserve the mixture in a glass-stoppered bottle. 



Mett's Tubes. 



See directions for making in chapter on gastric digestion. 



Millon's Reagent 



Digest 1 part (by weight) of mercury with 2 parts (by 



