432 ALBUMINOUS COMPOUNDS. 



greater quantity may be added to the other without turning it 

 red. and till it turns red no precipitate will fall. 1 



16. Alkali Albuminate should contain no Sulphur. 

 The sulphur which is contained in albumin is said to be re- 

 moved by the alkali used in converting it into alkali al humi- 

 liate, and it therefore differs from casein and syntonin, in both 

 of which sulphur is present. The presence of sulphur is thus 

 tested : Put a piece of alkali albuminate into liquor potassae, 

 add a drop of solution of lead acetate and boil. The solution 

 should not become brown, as it would do from the formation 

 of lead sulphide, if sulphur were present in the alkali albumi- 

 nate. The sulphur is, however, by no means always removed 

 during the preparation, and it is very probable that a brown 

 color will be got. 



SECTION III. ALTERATION OF ALBUMIN BY ACIDS. ACID ALBUMIN 

 OR SYNTONIN. 



When a solution of albumin is treated with very dilute acids, 

 or when solid albumin is dissolved in concentrated acids, it is 

 converted into acid albumin, which is identical with syntonin, 

 or, at any rate, appears to be so. Myosin, vitellin, and fibrin 

 are quickly dissolved by dilute acids, and converted into 

 S3*ntonin. It is soluble in very dilute acids, but is insoluble in 

 wati-r, and it is, therefore, precipitated by neutralization. It 

 is redissolved by excess of alkali, as it is soluble in alkalis 

 and alkaline carbonates. Unlike alkali albuminate, its pre- 

 cipitation is not prevented by the presence of alkaline phos- 

 phates. It is not precipitated from decidedly acid solutions 

 by boiling, but when the solutions are nearly neutralized, and 

 only very faintly acid, boiling precipitates it. 



1 It is usually stated that alkali albuminate is precipitated by neutral- 

 ization. In the text I have made use of this expression, which is per- 

 haps a convenient one, since the quantity of acid necessary to produce 

 precipitation being extremely small and the preeipitate soluble in excess, 

 the direction to neutrali/e rather than to acidulate, is more likely to 

 lead to the desired result. 1 believe the student will readily convince 

 himself that alkali albuminate is not precipitated from its solutions by 

 exact neutralization, and is only thrown down when a slight excess of 

 acid is present. I am inclined to think that the .-odium phosphate acts 

 simply by preventing the inadvertent addition of a slight excess of acid, 

 which is extremely liable to occur in solutions of alkali albuminate, and 

 that syntonin is precipitated by neutralization in presence of sodium 

 phosphate, while alkali albuminate is not, because the point of slight 

 acidity at which the albumin is precipitated is reached before that of 

 neutralization in the former case, so that, before neutralization is 

 etlected, the albumin is thrown down ; while in the latter, the solution 

 docs not become acid, and the albumin is therefore not precipitated, 

 till after neutralization. On this subject compare Rollett, Wien. Sitz. 

 Ber. XXXIX. p. 547, and Moleschott's Untersuch, VII. p. 230, also 

 Soxhlet, Journ. f. pract. Chemie, N. F. 1872, VI. p. 1. 



