GENERAL PROPERTIES AND REACTIONS OF PROTEIDS. 41 
simple method of separating the two classes of proteids. 1 If boiling is omitted, 
the proteoses are in part precipitated also (C. J. Martin). 
5. Tlie alcohol method. -The solution is rendered faintly acid with acetic acid, 
and several times its volume of absolute alcohol are added. After twenty-four 
hours it is boiled and filtered ; the filtrate is proteid-free.' 2 The action of alcohol 
mi proteids is peculiar ; it precipitates proteids in the cold ; and the precipitate, 
if washed free from alcohol, is found to be readily soluble in suitable reagents 
such as saline solution. But if the precipitate is left in contact with the alcohol 
for days or weeks, the solubility of the precipitate is lost ; the precipitate has 
been converted into a coagulum. This loss of solubility, however, does not 
occur with proteoses and peptone, and thus this is another very good though 
tedious method of separating native proteids from products of proteolysis. 3 
6. Salicylsulphonic-acid method. — This is recommended by McWilliam. 4 
The reagent precipitates albumins and globulins ; on heating, the precipitate is 
coagulated. The same reagent precipitates proteoses ; on heating, the precipitate 
dissolves, and re-appears on cooling. The reagent does not precipitate 
peptones. 
7. By boiling. — In some cases the proteids are precipitated or more properly 
coagulated by boiling after faintly acidulating the solution. This is the case 
with the albumins and globulins, and with the proteids which are usually 
found in morbid urines. For the separation of native proteids from proteoses 
and peptones, the method is not to be recommended, because boiling with even 
dilute acids leads to the formation of small quantities of these products of 
proteolysis. The use of this method has thus produced many mistakes ; it led 
Struve, Schmidt-Mulheim, and others, to the conclusion that a peptonedike 
substance exists in milk and in blood ; and more recently Chabrie, 5 by the use of 
the same method, has described a new proteosedike constituent of blood 
serum, to which he has given the name " albumone." Chabrie's mistake has 
been amply demonstrated by R. Brunner. 6 It should be added that Devoto's 
method is not wholly free from the same objection. 7 
For quantitative purposes the precipitate produced by these several 
methods may be collected, washed, dried, and weighed, then incinerated, 
and the ash deducted. Other methods that have been devised are 
densimetric methods, in which, after removal of the proteid, the loss of 
specific gravity is multiplied by a constant factor, 8 and methods in which, 
by Kjeldahl's process, a nitrogen estimation is made in the precipitate 
produced by some precipitant. Sebelien 9 recommends tannin for this 
purpose. 
Precipitation by neutral salts (German, Aussalzung). — There are a 
number of organic substances whicli can be precipitated from their 
1 Obermayer, Med. Jahrb., Wien, 1888, S. 375-381; Starling, Joum. Physiol., 
Cambridge and London, vol. xiv. p. 131 ; C. J. Martin, ibid., vol. xv. p. 375 ; Halliburton 
and Brodie, ibid., vol. xvii. p. 169 ; Halliburton and Colls, Joum. Path, ami Bacterial., 
Edin. and London, 1895, vol. iii. p. 295. 
" Hoppe-Seyler, "Handbucb," S. 312 ; Schmidt, Arch. f. d. cjes. Physiol., Bonn, Bd. 
xi. S. 10 ; Hoffman, Virchow's Archiv, 1879, November, S. 255. 
3 S. Martin, Gonlstonian Lectures, Brit. Med. Joum., London, 1892, vol. i. ; Gourlay, 
Joum. Physiol., Cambridge and London, 1894, vol. xvi. p. 32. 
4 Brit. Med. Joum., London, 1891, vol. i. p. 837 ; 1892, i. p. 115. The reaction was 
previously described by Roch, Pharm. Gevir.-Bl., Leipzig, 1889, S. 549. 
5 Compt. rend. Acad. d. sc., Paris, tome cxiii. p. 557. 
6 Inaug. Diss., Bern, 1894. 
7 M. Mattlies, Berl. klin. Wchnschr., Bd. xxxi. S. 351 ; Halliburton and Colls, 
loc. cit. 
8 Bornhardt, Ztschr. f. anal. Glum., Wiesbaden, 1870, S. 149; 1877,- S. 124 ; Huppert 
and Zahor, Ztschr. f. physiol. Chcm., Strassburg, Bd. xii. S. 467, 484. 
9 Ibid., Bd. xiii. S. 135 ; Konig and Kisch, Ztschr. f. anal. Chcm., Wiesbaden, Bd. 
xxvii. S. 191. 
