REAGENTS AND SOLUTIONS 629 



Basic Lead Acetate Solution. 1 This solution possesses the following 

 formula: 



Lead acetate 180 grams. 



Lead oxide (Litharge) no grams. 



Distilled water to make 1000 grams. 



Dissolve the lead acetate in about 700 c.c. of distilled water, with boiling. 

 Add this hot solution to the finely powdered lead oxide and boil for one- 

 half hour with occasional stirring. Cool, filter and add sufficient dis- 

 tilled water to the filtrate to make the weight i kg. 



Benedict's Solution. 2 Benedict has modified the Fehling solution 

 and has succeeded in obtaining one which does not deteriorate upon 

 long standing. It has the following composition: 



Copper sulphate 17.3 grams. 



Sodium citrate *73.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 800 c.c. of water. Pour (through a folded filter paper if neces- 

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

 copper sulphate in about 100 c.c. of water. Pour the carbonate- 

 citrate solution into a large beaker or casserole and add the copper 

 sulphate solution slowly, with constant stirring and make up to one 

 liter. The mixed solution is ready for use and does not deteriorate upon 

 long standing. 



Benedict's Sugar Reagent. 3 



Copper sulphate (crystallized) 18 .o grams. 



Sodium carbonate (crystallized, one-half the weight of the 



anhydrous salt may be used) 200.0 grams. 



Sodium or potassium citrate 200 . o grams. 



Potassium thiocyanate 125.0 grams. 



Potassium ferrocyanide (5 per cent solution) 5.0 c.c. 



Distilled water to make a total volume of 1000.0 c.c. 



With the aid of heat dissolve the carbonate, citrate and thiocyanate 

 in enough water to make about 800 c.c. of the mixture and filter if 

 necessary. 



Dissolve the copper sulphate separately in about 100 c.c. of water 

 and pour the solution slowly into the other liquid, with constant stirring. 

 Add the ferrocyanide solution, cool and dilute to exactly i liter. Of the 

 various constituents, the copper salt only need be weighed with exact- 

 ness. Twenty-five c.c. of the reagent are reduced by 50 mg. of glucose. 



1 Indican determination, p. 558. 



2 Benedict's modification of Fehling's test, pp. 26 and 435. 

 8 Quantitative determination of sugar, p. 538. 



