xi THE ALBUMINOIDS : GELATINE 563 



according to Klug 1 and Hofmeister 2 a feeble yellow colour after 

 treatment with nitric acid. Both these reactions must be caused by 

 the presence of foreign substances. The lead sulphide reaction is 

 given by commercial gelatine, but is absent in purified gelatine, 

 according to Morner. 3 The reaction of Molisch has been observed by 

 Klug l and Hofmeister, 2 while that of Adamkiewicz is absent, owing 

 to gelatine not containing any tryptophane. 



The precipitation-reactions of non-dissociated gelatine have been 

 described by Klug, 1 Morner, 3 and others, while those for the glutoses 

 have been investigated by Klug 1 and Hofmeister. 2 Gelatin is not 

 precipitated by nitric acid or other mineral acids, nor on being acidified 

 with acetic or hydrochloric acid. Neither do neutral lead acetate, 

 silver nitrate, copper sulphate, ferric chloride, or alum, precipitate. 

 On the other hand, the chlorides of gold and platinum and stannous 

 chloride give precipitates, which are soluble at the boiling temperature 

 and which return on cooling. Mercuric nitrate and basic lead acetate 

 cause a precipitate, as does also mercuric chloride in the presence 

 of HC1 or of neutral salts. The alkaloidal reagents, taken as a whole, 

 also cause precipitation ; the phospho-molybdic acid precipitate is per- 

 manent when heated, while the precipitates formed by picric acid, 

 tannic acid, chromic acid, mercury + potassium iodides + HC1 are dis- 

 solved by heating, and return on cooling. Bromine- and chlorine 

 water and potassium iodide also precipitate. With tannic acid 

 salt-free gelatine gives no precipitate, and in this resembles salt-free 

 albumin-solutions; on the addition of salt, however, a precipitate is 

 formed. 4 The same holds good for alcohol. Till a short time ago it 

 was considered characteristic of solutions of gelatine that, in contrast 

 to other albumins, they gave no precipitate with potassium ferro- 

 cyanide + acetic acid, 5 but Morner 4 has shown that under 30 C. it 

 is possible to obtain a precipitate with very dilute solutions, but that 

 the precipitate is dissolved by both an excess of gelatine or of ferro- 

 cyanic acid, and also that the presence of salts, organic acids, or bases 

 or urea prevents the formation of a precipitate. Gelatoses never give 

 a precipitate. The behaviour of gelatine towards neutral salts has 

 been investigated but little ; it is precipitated by not quite saturated 



1 F. Klug, Pflugers Arch.f. d. ges. Physiol. 48. 100 (1891). 



2 F. Hofmeister, Zeitschr.f. physiol. Chem. 2. 299 (1878). 



3 C. T. Morner, ibid. 28. 471 (1899) ; see also ibid. 18. 213 (1893) and Skandinav. 

 Archiv. f. Physiol. 1. 210 (1889). 



4 C. T. Morner, Zeitschr. f. physiol. Chem. 28. 471 (1899) ; see also ibid. 18. 

 213 (1893) and Skandinav. Arch. f. Physiol. 1. 210 (1889) ; H. Weiske, Zeitschr. f. 



1. Chem. 7. 460 (1883). 



5 J. Miiller, Liebig's Annalen, 21. 277 0837). 



