224 GLUCOSES, SACCHAROSES, ETC. 



acid, into aspartic acid and ammonia ; the former of which is 

 lievo-rotatory in alkaline solution, but dextro-rotatory in acid. 



Asparagine is not precipitated by basic acetate of lead, by lime, 

 or by baryta ; and although aspartic acid is thrown down by lead 

 salts, yet the precipitate is redissolved by an excess. 1 



211. Estimation of three Sugars. Dupre 2 and Apjohn 3 have 

 made the estimation of cane-, grape-, and fruit-sugar in the same 

 solution, the subject of investigation. As their methods, how- 

 ever, involve a combination of optical and volumetric determina- 

 tions in which accuracy is required in ascertaining the amount of 

 grape- and fruit-sugar present, especially in titrating, I am afraid 

 their processes will at present yield only approximate results. I 

 have already shown ( 85) that the volumetric estimation of 

 glucose in the presence of cane-sugar is not so accurate as might 

 be wished. 



212. Mannite. Of mannite (cf. 91) it may be here observed 

 that one part dissolves in 6'14 to 6 '21 of water at 15, and in 5*12 

 to 5*38 at 20. One part requires also 1515 of absolute alcohol 

 at 17* for complete solution. Although optically inactive, as 

 previously stated, it is dextro-rotatory when dissolved in a con- 

 centrated solution of borax. It melts at 166, and is converted at 

 200 with loss of water into mannitan. With moderately strong 

 nitric acid it yields principally mucic and saccharic acids ; with the 

 strongest acid, nitro-mannite. It is said (according to Biegel) to 

 reduce gold and silver salts, but not alkaline copper solution, when 

 warmed for a short time. Mannite prevents, however, the preci- 

 pitation of hydrate of copper. 



1 On saccharometry, and especially the estimation of invert-sugar when 

 accompanied by cane-sugar, as in beet-juice, crude sugar, etc., see Ventzke, 

 Journ. f. pract. Chem. xxv. 65, xxviii. 101 ; Kleinschmidt, Dingler's polyt. 

 Journ. clxxxi. 306, 1867 ; Anders, ibid, clxxxii. 331 ; Bodenbender, 

 Zeitschr. f. Chem. N. F. ii. 222, 1867 ; Sostmann, ibid. 480. The latter 

 authors draw special attention to the influence that lime exercises on the 

 results of optical determinations of cane-sugar. The influence of asparagine 

 and aspartic acid has been observed by Dubrunfaut (Dingler's polyt. Journ. 

 cxxi. 305) and Scheibler, ibid, clxxxi. 415). Communications by Scheibler on 

 the errors in optical estimations have appeared in the Zeitschr. f. Chem. N. F. 

 iii. 617, and Zeitschr. f. anal. Chem. viii. 211, 1869. See also Stammer, 

 Dingler's polyt. Journ. clxxxii. 160 ; Dubrunfaut, ibid. cxxi. 299, clxxxv. 231 ; 

 Landolt, Zeitschr. f. anal. Chem. vii. 1, 1868. On the influence of asparagine, 

 see lastly also Champion and Pellet, ibid. xvi. 120, 1877. 



2 Chem. News, xxi. 97, 1870, 



3 Ibid. p. 86. See also Zeitschr. f. anal. Chem. ix. 499, 501, 1870. 



