REAGENTS AND SOLUTIONS 597 



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. 



Benedict's Sulphur Reagent. 



Crystallized copper nitrate, sulphur-free or of known sulphur 



content 200 grams. 



Sodium or potassium chlorate 50 grams. 



Distilled water to 1000 c.c. 



Benzidine Solutions for Volumetric Sulphur Determinations. 



(a) Rosenheim and Drummond. Rub 4 grams of benzidine (Kahl- 

 baum) into a fine paste with about 10 c.c. of water and transfer to a 

 2-liter flask with the aid of about 500 c.c. of water. Add 500 c.c. of con- 

 centrated HC1 (sp. gr. 1.19) and make up to 2 liters with distilled 

 water. 150 c.c. of this solution, which keeps indefinitely, are sufficient 

 to precipitate o.i gram H 2 SO 4 . 



(b) Raiziss and Dubin. Put 6.7 grams of benzidine (Merck Reagent) 

 in a i-liter flask, add 29 c.c. of hydrochloric acid (sp. gr. 1.12) and dilute 

 up to the mark. 



Bertrand Sugar Reagents. 1 (a) Copper Sulphate Solution. Forty 

 grams of pure crystallized copper sulphate are dissolved in water to 

 make a liter. 



(b) Dissolve 200 grams of Rochelle salts and 150 grams of NaOH in 

 water to make 1000 c.c. 



(c) Acid Ferric Sulphate Solution. Dissolve 50 grams of ferric sul- 

 phate in about 200 c.c. of water and pour into this a mixture of 200 c.c. 

 of concentrated sulphuric acid diluted with about 400 c.c. of water. 

 Mix and make to 1000 c.c. 



(d) Potassium Permanganate Solution. Dissolve 5 grams of potas- 

 sium permanganate in water to make 1000 c.c. Standardization. 

 Dissolve 0.250 gram of ammonium oxalate in 50-100 c.c. of water add 

 1-2 c.c. of concentrated sulphuric acid and titrate with the permangan- 

 ate to a rose color. Multiply the number of grams of oxalate used by 

 0.895 to get the equivalent in Cu of the number of cubic centimeters of 

 permanganate used. Calculate the Cu value of i c.c. 



1 Determination of sugar, p. 527. 



