i REACTIONS OF ALBUMINOUS SUBSTANCES 13 



phenol is the best precipitant, and the higher a member in this series, 

 the less does it precipitate, and stronger solutions of all aromatic 

 alcohols redissolve the originally formed precipitate (Spiro l ). Acetone 

 and chloroform precipitate as does alcohol. 2 



The processes of salting out and of heat precipitation will be dis- 

 cussed in Chapter VII. 



With a number of acids and bases albuminous bodies form quite 

 or almost insoluble bodies, and are therefore precipitated from their 

 watery solutions. This reaction is characteristic of all natural albu- 

 minous substances, the complex albumins, and, for the most part, all 

 derivatives which still resemble albumins, such as the albumoses. The 

 further a derivative of an albumin is removed from its natural state, 

 the more difficult does it become to precipitate it, as will be more 

 fully described in Chapter IV. 



1. Precipitation of Albuminous Substances by Salts of the Heavy Metals 



Albumins, being potential acids because of their amino-acid nature, 

 are precipitated by the salts of the heavy metals as insoluble metallic 

 albuminates from acid, neutral, or alkaline solutions. The precipitation 

 is always a complete one, and the precipitate is as a rule insoluble in 

 an excess of the reagent when we are dealing with the albumins proper, 

 while some of the proteid derivatives, such as albumoses, may re- 

 dissolve. The myogen of muscle is an exception, as it is not precipi- 

 tated by the heavy metals in the absence of alkali salts (Fiirth 3 ). 

 The same holds good for haemoglobin, 4 and may hold good for other 

 albuminous substances (Cohnheim). 



Nearly all the heavy metals precipitate, but those commonly 

 employed are : 



1. Ferric chloride and ferric acetate; they were used by P. 



Muller, 5 Schmidt -Miilheim, 6 Siegfried, 7 and others. With 

 excess of ferric chloride the precipitates are apt to redissolve. 

 Rose 8 was the first to describe a jelly-like compound formed 

 by the union of albumin with ferric chloride. 



2. Copper sulphate and the still more sensitive copper acetate. 



1 K. Spiro, Hofmeister's Beitr. IV. 300 (1903). 



2 E. Salkowski, Zeitschr. /. physiol. Chem. 31. 329 (1901). 



3 0. v. Fiirth, Archivf. experiment. Patholog. und Pharmak. 36. 231 (1895). 



4 F. N. Schulz, Zeitschr. f. physiol. Chem. 29. 86 (1899). 



5 P. Muller, ibid. 26. 48 (1898). 



J'' 6 Schmidt-Miilheim, Arch. f. (Anat. u.) Physiol. 1880, p. 33. 



V ' 7 M. Siegfried^ Zeitschr. f. physiol. Chem. 21. 360 (1895), and Arch. f. (Anat. 

 u.) Physiol. 1894, p. 401. 8 Ferdinand Rose, Poggendor/'s Ann. 28. 140 (1833). 



