230 QUANTITATIVE ANALYSIS 



the Carbohydrates in the Faeces/ 7 page 213.) If the sugar 

 is to be determined gravimetrically, take 50 cc. of the Feh- 

 ling's solution, 100 cc. of water, and 25 cc. of the solution ulti- 

 mately obtained from the bread. For further details of the 

 methods consult the earlier chapters. 



According to L. Liebermann l this method gives too low- 

 results on account of the destruction of sugar by the long- 

 continued heating. He recommends the following method: 

 About 10 g. of the substance are boiled for one and one-half 

 hours on a sand-bath with 100 cc. of 2 per cent, hydrochloric 

 acid in a 250-300-cc. flask connected with a reflux condenser. 

 Then the fluid is almost neutralized with sodium hydroxide 

 solution, filtered into a liter measuring-flask, rinsing and 

 washing with hot water. Dilute to one liter and take out 20 

 cc. for the sugar determination with Fehling's solution. 

 According to L. Liebermann there is no danger of the 2 per- 

 cent, hydrochloric acid converting the cellulose into sugar. 

 Instead of filtering and washing, the fluid, together with sus- 

 pended material, may be diluted to one liter and then filtered 

 through a dry filter. 



Liebermann uses a peculiar method for the determina- 

 tion of the cuprous oxide. The precipitated oxide is filtered 

 off, washed, dissolved in hydrochloric acid, and the solution 

 reduced in a weighed platinum dish with a small piece of 

 zinc. The liquid is poured off from the precipitated copper, 

 which is then washed a few times with water, alcohol, and 

 ether, dried at 100 and weighed. 



For the phosphorus determination fuse 1.5 to 1.8 g. with. 

 30 g. of the oxidizing mixture (30-35 cc. of nitric acid). 



1 Maly's Jahrb. f. Thierchemie, 1886, 55. 



