Power of Crystalline Ovalbumin and Serum Albumin. 



17 



Hopkins alone obtained a constant value for successive recrystallisations. 

 The earlier figures were obtained from material crystallised but once, and by 

 the inferior technique of Hofmeister in most cases. 



The last worker on the subject claims that the true value is higher than 

 — 30 - 7°and attributes her average result of — 31'0°as due to a more sensitive 

 test for the presence of sulphate ions, thus allowing of more thorough 

 washing of the coagulated albumin before drying and weighing. The tech- 

 nique which I have adopted in obtaining the following observations involved 

 the use of a 400-mm. polarimeter tube, so that very large rotations were 

 observed. A large Hilger polarimeter was employed and observations were 

 made both with the sodium flame and with the green band of the quartz 

 mercury-vapour lamp. The solutions used were made as concentrated as 

 possible, being about 10 per cent, strength. The analysis of these solutions 

 for their content of albumin was carried out in the first series by the Devoto 

 method, using accurately calibrated pipettes for volume measurement of a 

 quantity of solution sufficient to yield about - 5 grm. of dried coagulum, and 

 Kahlbaum's purest (NH^SO^ in saturated solution as coagulating agent. 

 This solution is naturally acid, having a Ph of 5 - 5 or less. Coagulation was 

 brought about by placing the solution to which the albumin had been added 

 for 1 hour on a boiling water bath. After cooling, the precipitate was filtered 

 off on to hardened filter paper and washed with cold water until free from 

 sulphate. Finally, the precipitate was removed quantitatively to a platinum 

 basin by means of a few cubic centimetres of distilled water, the excess 

 water was evaporated on a water bath, and the protein dried until of constant 

 weight in a Lothar Meyer air bath at 110° C. 



The removal of the last traces of sulphate from the precipitate is a 

 difficult operation. I have tested the sensitivity of the BaCl 2 test for 

 sulphates, applied as a ring and in the direct way, on a series of dilutions of 

 normal H2SO4. When carried out as a ring test, using a saturated solution 

 of BaCl2 and allowing the tubes to stand 15 minutes before decision, the test 

 is sensitive to one part in one million. The same limit was found for the 

 test when applied by adding five drops to about 20 c.c. of filtrate and 

 allowing to stand 15 minutes. An approximate idea of the quantity of 

 sulphate being removed can be obtained in the final stage of washing by 

 comparison of the turbidity obtained with that given by known strengths of 

 H2SO4. By continuous washing, I have never been able to remove the last 

 traces of sulphate in less than 4 days. This point is discussed below. If 

 any protein goes back into solution during this long period of washing, the 

 amount must be negligible, for I have repeatedly tested the filtrates for 

 protein with negative results, and evaporated down quantities of the filtrate 



vol. xciii. — b. c 



