234 ALBUMINOIDS. 



can therefore be made available for the separation of the acid; 

 the basic lead-salt can be converted into the normal by the action 

 of dilute nitric acid. Glycolic acid can be isolated by shaking 

 with ether. Its calcium-salt contains 23'09 per cent, of oxide of 

 calcium, its normal lead-salt 62*48 per cent, of oxide of lead. 



ALBUMINOIDS, ETC. 



§ 224. Estimation. — In § 96 the albuminoids have been estimated 

 by multiplying the nitrogen found by 6*25. This calculation is 

 based upon the assumption that albuminoid substances contain 

 16 per cent, of nitrogen. ^ Attention has, however, been frequently 

 drawn to thefact,thatmost albuminous substances contain more than 

 16 per cent, of nitrogen; those of cereals, leguminous fruits, etc., 

 can be estimated to contain at least 16*60 per cent. ; the factor 6'0 

 has therefore been recommended in such cases as preferable. But 

 even then the results obtained will be too low if the material 

 under examination contain much conglutin or gliadin^ (as, for 

 instance, lupin seeds, almonds, brazil-nuts, wheat, etc.), as 

 conglutin contains 18-4, and gliadin (§235) 18-1 per cent, of 

 nitrogen. When, therefore, large quantities of those bodies are 

 present, Bitthausen advises multiplying by 5'5. 



§ 225. Legumin. — If the experiment described in § 93 has shown 

 the presence of legumin (vegetable casein), the maceration should 

 be repeated in the cold (best at a temp, of 4° to 5°) for about 

 five hours, the clear liquid decanted off, and the maceration 



^ It was formerly assumed that they contained 15 6 per cent, of nitrogen, 

 and the amount of the latter was therefore multiplied by 6*33. That the 

 nitrogen found in alkaloids, albuminoids, etc., by the method of Varrentrapp 

 and Will is too low has already been shown by V. d. Burg (Zeitschr. f. anal. 

 Chem. iv. 322, 1865), Nowak (ibid. xi. S24, 1871), apd Seegen and Nowak 

 (ibid. xii. 316, 1873 ; xiii. 460, 1874). Meusel expresses himself to the con- 

 trary (ibid. v. 197,' 1866). Marcker has shown (AnnaL d. Landwirthsoh. xii. 

 619) that the error is not so large if the soda lime used is free from magnesia. 

 See also Kreusler (Zeitschr. f. anal. Chem. xii. 354, 1873) ; Marcker (ibid 

 221); Marcker und Abesser (ibid. 447); Johnson (ibid. 446); Kitthausen 

 (ibid. xiii. 240, 1874); Settegast (ibid. xvii. 501, 1878). On the estima- 

 tion of nitrogenj see also Nowak (Zeitschr. f. anal. Chem. xii. 102,1873); 

 Makris (ibid. xvi. 249, 1877); Habermann (ibid. xvii. 876, 1878); Pfl%er 

 (Archiv. f. ges. Phys. xviii. 117, 1879) ; Hanko (Ber.d. d. chem. Ges. xii 

 451) ; Sohiff (Annal d. Chem. und Pharm. oxcv. 293) ; Bitthausen (Zeitscht 

 t. anal. Chem. xviii. 601, 1879). 



' Compare Kitthausen, Die Eiweisskorper der Getreidearten, Hulsenfriichtu 

 etc., 287, Bonn, 1872. 



