278 METHODS OF ANALYSIS [Chap. 



SUGAR^.-TENTATIVE. 



22 REAGENTS. 



(a) Mercuric nitrate solution. — Warm 220 grams of yellow mercuric oxid with 

 300 cc. of water and treat with small portions of nitric acid, stirring until dissolved. 

 Make up to 1 liter and filter. 



(b) Phosphotungstic acid solution. — Prepare a 20% solution of phosphotungstic 

 acid in 2.5% hydrochloric acid. 



23 DETERMINATION. 



Boil 100 grams of the sample with about 350 cc. of water for about 20 minutes, 

 cool, add an excess (10-30 cc.) of the mercuric nitrate solution, nearly neutralize 

 with sodium hydroxid solution and make up to 500 cc, exclusive of fat. Mix thor- 

 oughly, allow the mixture to settle and decant the clear liquid through a large, dry, 

 folded filter. To an aliquot of the filtrate add 1-2 cc. of concentrated hydrochloric 

 acid for each 100 cc, heat to boiling and saturate thoroughly with a rapid current 

 of hydrogen sulphid. Remove the excess of hydrogen sulphid by means of a cur- 

 rent of air, cool, make up to a definite volume with water and filter. To an aliquot 

 of the filtrate add an excess of the phosphotungstic acid solution, noting the in- 

 crease in volume of the solution caused by this addition and place in an ice box 

 for several hours or overnight. Filter, introduce 50 cc of the filtrate into a 400 cc. 

 beaker, neutralize with concentrated sodium hydroxid solution, add 50 cc. of Soxh- 

 let's solution [VIII, 19], heat so that boiling begins in 4 minutes, boil 2 minutes and 

 filter through an alundum crucible of suitable porosity, using very gentle suction. 

 If the filtrate is green or yellow, refilter through the same crucible until the fil- 

 trate is clear blue. Wash the precipitate with a very small amount of 5% sodium 

 hydroxid solution, refiltering the washings if they are turbid. Dissolve the precipi- 

 tated cuprous oxid in nitric acid (1 to 1) and determine copper as directed under 

 VIII, 29. Find the corresponding amount of dextrose or invert sugar from VIII, 

 27, and calculate the per cent in the original sample by proper correction for the 

 various aliquots taken in the determination. To convert invert sugar to sucrose 

 multiply by the factor 0.95. 



NITRATES. 

 Sclildsing-W agner Method^. — Tentative. 



2A REAGENT. 



Ferrous chlorid solution. — Dissolve nails or other small pieces of iron in concen- 

 trated hydrochloric acid, keeping an excess of iron present until the evolution of gas 

 ceases. Keep the solution in 50 cc. glass-stoppered bottles entirely filled. Employ 

 only freshly opened bottles of the reagent for the determination. 



25 APPARATUS. 



Provide a 250 cc. flask with a 2-holed rubber stopper. Through one of the holes 

 pass the stem of a funnel having a glass stop-cock, and into the other fit a delivery 

 tube leading downward at an angle from the flask to a trough containing water. 

 Terminate the upper end of the delivery tube just below the rubber stopper in 

 the flask and place the lower end under the surface of the water in the trough, the 

 exit being immediately beneath the mouth of an inverted measuring tube, filled 

 with 40% potassium hydroxid solution. Cover the trough end of the delivery tube 

 with a piece of rubber tubing. Midway on the delivery tube between the flask and 

 the measuring tube place a short length of rubber tubing and a pinch-cock. 



