642 PHYSIOLOGICAL CHEMISTRY 



the filtrate in a large flask. To the hot filtrate add 100 c.c. of concen- 

 trated sulphuric acid, previously diluted with about two volumes of 

 water. The liberated picric acid begins to come out at once. Put a 

 beaker over the mouth of the flask and cool under running tap water to 

 about 3oC. Filter with suction as before and wash free from sul- 

 phates with distilled water. 



(b) Method of Halverson and Bergeim. To 50 gm. of picric acid add 

 700 c.c. of distilled water. Boil until clear and while boiling add 

 10 c.c. of concentrated hydrochloric acid. Cool. Wash by decanta- 

 tion with 100 c.c. of distilled water. Repeat the recrystallization. 

 Transfer to a Buchner funnel and wash with about 150 c.c. of water. 

 Dry in a desiccator or between filter papers. 



Picric Acid, Saturated Solution. 1 This may be prepared either by 

 allowing distilled water to stand in contact with an excess of picric 

 acid with occasional shaking, or by making a 1.2 per cent solution. 



Picric Acid and Sodium Picrate Solution. 2 Place 36 gm. dry pow- 

 dered picric acid in a liter flask or stoppered cylinder, add 500 c.c. of 

 i per cent sodium hydroxide solution and 400 c.c. of hot water. Shake 

 occasionally until dissolved. Cool and dilute to one liter. 



Roberts' Reagent. 3 Mix i volurhe of concentrated nitric acid and 

 5 volumes of a saturated solution of magnesium sulphate. 



Rosenheim's lodo-Potassium Iodide Solution. 4 Dissolve 2 grams 

 ofiodine and 6 grams of potassium iodide in 100 c.c. of water. 



Sahli's Reagent. 6 This reagent consists of a mixture of equal parts 

 of a 48 per cent solution of potassium iodide and an 8 per cent solution of 

 potassium iodate. 



Salted Plasma. 6 Allow arterial blood to run into an equal volume 

 of a saturated solution of sodium sulphate or a 10 per cent solution of 

 sodium chloride. Keep the mixture in the cold room for about 24 

 hours. 



Schweitzer's Reagent. 7 Add potassium hydroxide to a 5 per cent 

 solution of copper sulphate which contains 5 per cent ammonium 

 chloride. Filter off the precipitate of cupric hydroxide, wash it, and 

 bring 3 grams of the moist cupric hydroxide into solution in a liter of 

 20 per cent ammonium hydroxide. 



Seliwanoff's Reagent. 8 Dissolve 0.05 gram of resorcinol in 100 c.c. 

 of dilute (1:2) hydrochloric acid. 



1 Determination of creatinine in blood p. 280 and urine p. 526. Also qualitative tests. 



2 Determination of sugar in blood p. 287. 



3 Roberts' ring test, pp. 103 and 440. 



4 Rosenheim's periodide test, p. 374 

 6 Determination of free acid, p. 167. 



6 Experiments on blood plasma, p. 271. 



7 Schweitzer's solubility test, p. 48. 



8 Seliwanoff's reaction, pp. 34 and 462. 



