BEHAVIOR TOWARD NEUTRAL SALTS. 33 



a saturated neutral solution of ammonium sulphate, the mixture 

 being diluted in each case to 10 c.c. with distilled water. The con- 

 tents of each tube are thoroughly mixed and set aside for one-half 

 hour, when a further examination is made. In the first series it is 

 well to start with a set of tubes containing 0.5, 1.0, 1.5, 2.0, 2.5, 

 etc., c.c. of the sulphate solution. At the end of a half hour the 

 contents of each tube are passed through small filters and the 

 filtrate treated with an additional -^ c.c. of the salt solution. Sup- 

 posing that tube 1 containing 0.5 c.c. presented no turbidity, but 

 that this was marked in tube 2, then it is manifest that the lower 

 limit of precipitation lies between 0.5 and 1. If now the filtrate 

 of tube 1 after the addition of 0.1 c.c. of the salt solution and 

 standing shows a turbidity, the lower limit for this particular albumin 

 is called 0.6. In a similar manner the upper limit is determined. 

 Supposing that the filtrate of the tube containing 3.5 c.c. of salt 

 solution becomes turbid on adding 0.1 c.c. further, while in the 

 filtrate of a tube containing 3.6 c.c. salt solution from the first, no 

 turbidity developed, it is clear that 3.6 represents the upper limit. 



In the following table the limits of precipitation of some of the 

 more important albumins have been collected : 



Lower limit. Upper limit. 



Nucleo-albumins 0.1-0.6 1.6-2.3 



Fibrinogen 1.5-1.7 2.5-2.7 



Fibrinoglobulin 2.2 2.9 



Euglobulin 2.8 3.3 



Pseudoglobulin 3.4 4.6 



Serum-albumin 6.4 9.0 



Especially characteristic and constant is the upper limit, while 

 the lower limit occasionally fluctuates somewhat. In acid solu- 

 tions there is a general lowering of the limits of precipitation ; in 

 this case the albumins are not precipitated as such, but as salts, the 

 albumins playing the part of a base. 



After precipitation the albumins tenaciously hold a certain 

 amount of the salt, which can scarcely be removed, even on pro- 

 longed dialysis. Noteworthy also is the fact that certain albumins 

 are capable of abstracting the acid of the particular salt which is 

 employed, to form compounds from which the acid in question 

 cannot be removed on washing with water. This peculiarity is 

 especially well marked in the case of serum-albumin, and probably 

 accounts for the observation that on repeated crystallization from 

 ammonium sulphate solution the mixture of albumin and sulphate 

 becomes more and more acid, while at the same time ammonia is 

 liberated (G. Meyer). Such acid compounds of proteins can appar- 

 ently also occur in nature, as has been shown in the case of horn 

 and human hair (Morner). This property of abstracting acids from 

 the corresponding salts and uniting therewith should not be con- 

 founded with the power of certain albumins of combining with 

 free acids directly, which has been demonstrated by Sjoqvist, Cohn- 



