50 THE PROTEINS. [CH. II. 



This protein is known as ovo-mucoid. It is not coagu- 

 lated by boiling, nor precipitated by acetic acid. It is 

 precipitated by saturation with ammonium sulphate, and 

 also by strong alcohol. 



42. The crystallisation of egg-albumin. (Hopkins' method.) 

 Separate the white from a number of new-laid eggs, taking care not to 

 allow any of the yolk to mix with the white. Measure the egg-white 

 and churn it up with an exactly equal volume of a neutral fully- 

 saturated solution of ammonium sulphate by means of a whisk, 

 adding the sulphate in portions and mixing thoroughly after every 

 addition. Notice the strong smell of ammonia that is evolved. 

 Filter the mixture through a large pleated filter-paper. Measure 

 the filtrate. Take 100 cc. of it and cautiously treat it with 10 per 

 cent, acetic acid from a burette, noting the original level of the acid 

 in the burette. Add the acid a drop or two at a time, shaking gently 

 the whole time, until the precipitate produced at each addition no 

 longer dissolves on shaking, and the whole mixture is rather opale- 

 scent. This point is usually somewhat difficult to determine, owing 

 to the large number of air-bubbles that become suspended in the 

 fluid and closely resemble a fine precipitate. When you are satisfied 

 that a permanent precipitate has been produced, run in i cc. of the 

 acid in addition to the amount already added. A heavy white precipi- 

 tate is thus produced. Note the amount of acid that has been used 

 for the portion of 100 cc., and treat the remainder of the filtrate with 

 a corresponding amount of acid. Mix the two portions thoroughly 

 and allow to stand overnight. Note that the precipitate has in- 

 creased somewhat in amount. Mount a drop of the suspension on a 

 slide, cover with a slip, but do not press. Examine under the high 

 power of the microscope, and note the aggregation of very fine 

 needles. 



The albumin can be recrystallised by filtering, dissolving in as 

 small an amount of water as possible, filtering again, and cautiously 

 adding to the filtrate saturated ammonium sulphate till a faint 

 permanent precipitate is produced. If the mixture be allowed to 

 stand for some hours the albumin will separate out as fine needles. 



NOTES. i. For the experiment to succeed it is absolutely essential that 

 all theTeggs employed be perfectly fresh. One rather stale egg may interfere 

 with ^the crystallisation of a large number of fresh eggs. 



