254 BACTERIOLOGICAL METHODS 



The following methods for making the albumen solution are 

 submitted. 



i. Gravimetric Method A. Place 2 grams of pure powdered 

 egg albumen in 100 cc. of boiled distilled water, shake and set 

 aside for 6 to 12 hr., shaking frequently. Filter through a 

 tared filter paper which has been dried (at 100 C.) to constant 

 weight. Filtering is slow, requiring perhaps i hr. time. 

 When the last drop has filtered through, dry the filter paper, 

 with the unfiltered albumen residue upon it, to constant weight 

 and weigh. Deduct from this weight the weight of the dried filter 

 paper to obtain the weight of the albumen residue. From i 

 gram of egg albumen dried to constant weight determine the 

 percentage of moisture. From the data thus obtained it is easy 

 to determine the amount of boiled distilled water which must be 

 added to the filtrate (100 cc.) to make i per cent, dried albumen 

 solution. 



We will suppose that the dried filter paper to be used in filtering 

 the albumen solution weighs 1.570 grams and this same paper with 

 the undissolved albumen residue (also dried at 100 C. to constant 

 weight) weighs 1.965 grams, then the weight of the undissolved 

 dried albumen residue equals 0.395 gram. We will suppose that 

 i gram of albumen loses 0.126 gram on drying, or 12.6 per cent, 

 moisture. 0.395 gram raised to its normal air moisture (0.395 

 gram + 12.6 per cent of 0.395 gram = 0.444 gram) and subtracted 

 from 2.00 grams leaves 1.556 grams, the amount of albumen that 

 passed through the filter paper. 12.6 per cent, of 1.556 grams = 

 0.196 gram, and 1.556 grams less 0.196 gram = 1.360 grams which 

 represents the amount of albumen, dried to constant weight, that 

 passed into solution. Therefore to make a i per cent, solution it 

 is necessary to add enough boiled distilled water to the filtrate to 

 make i : 100. In this case add water up to the 136.00 cc. mark. 

 We now have a i per cent, solution sufficiently accurate for all prac- 

 tical purposes. 



This albumen test solution is now ready for use but it must be 



