APPENDIX. 417 



bonate and 173 grams of Rochelle salt dissolved in water and made 

 up to 500 c.c. 



These solutions should be preserved separately in rubber-stop- 

 pered bottles and mixed in equal volumes when needed for use. 

 This is done to prevent deterioration. 



Second Modification. Very recently Benedict has further modi- 

 fied his solution and has succeeded in obtaining one which does. not 

 deteriorate upon long standing. It has the following composition : 



Cupric sulphate 17.3 grams. 



Sodium citrate i?3-O grams. 



Sodium carbonate 100.0 grams. 



Distilled water to make i liter. 



With the aid of heat dissolve the sodium citrate and carbonate 

 in about 600 c.c. of water. Pour (through a folded filter paper if 

 necessary) into a glass graduate and make up to 850 c.c. Dissolve 

 the cupric sulphate in about 100 c.c. of water and make up to 150 

 c.c. Pour the carbonate-citrate solution into a large beaker or 

 casserole and add the cupric sulphate solution slowly, with constant 

 stirring'. The mixed solution is ready for use and does not dete- 

 riorate upon long standing. 



Benedict's solution as used in the quantitative determination of 

 sugar consists of three separate solutions, the two mentioned under 

 First Modification and in addition a potas-sium ferro-thiocyanate 

 solution. This third solution contains 15 grams of potassium fer- 

 rocyanide, 62.5 grams of potassium thiocyanate and 50 grams of 

 anhydrous sodium carbonate dissolved in water and made up to 500 

 c.c. In preparing the Benedict's solution for quantitative work the 

 three solutions mentioned are combined in equal parts. 



Black's Reagent. 1 Made by dissolving 5 grams of ferric chlor- 

 ide and 0.4 gram of ferrous chloride in 100 c.c. of water. 



Boas' Reagent. 2 Dissolve 5 grams of resorcin and 3 grams of 

 sucrose in 100 c.c. of 95 per cent alcohol. 



Congo Red. 8 Dissolve 0.5 gram of congo red in 90 c.c. of 

 water and add 10 c.c. of 95 per cent alcohol. 



Ehrlich's Diazo Reagent. 4 Two separate solutions should be 

 prepared and mixed in definite proportions when needed for use. 



(a) Five grams of sodium nitrite dissolved in I liter of distilled 

 water. 



1 Black's reaction, page 332. 



2 Test for free acid, page 124. 



3 Test for free acid, page 124. 



* Ehrlich's diazo reaction, page 342. 

 28 



