94 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



spending to the volume of gas is calculated in the usual way ; the 

 results are divided by 2 (see equation, p. 85). The weight may be 

 taken from the table compiled by Van Slyke and reproduced on p. 1 36. 



Each milligram of amino substance gives off from 1*7-1 '9 c.c. of 

 nitrogen. 



A correction should be made for the air 0*2 c.c. dissolved in 10 

 c.c. amino solution, i.e., allowing for the oxygen which combines with 

 the nitric oxide forming peroxide and is absorbed by the permangan- 

 ate, O'i6 c.c. must be deducted from the volume of gas. This correc- 

 tion is equivalent to 0-09 mgm. of amino nitrogen. No correction 

 is necessary, if air-free water be used in preparing the amino solution. 



If proteins or other solutions which may froth are to be analysed, 

 a few drops of capryl alcohol are first introduced into D through B, and 

 capryl alcohol can be added subsequently from B. 1 



Except lysine, the natural amino acids all react quantitatively in 

 five minutes : half an hour is required for this substance. Ammonia 

 and methylamine require one and a half to two hours, purines and 

 pyrimidines two to five hours, and urea eight hours. With these sub- 

 stances the apparatus is allowed to stand for the required time and 

 then shaken for two minutes. 



The completeness of the reaction may be tested by repeating the 

 process and ascertaining if more gas is evolved. 



Glycine and cystine evolve a larger volume of gas than the theoret- 

 ical ; the factor '926 may be used in estimating cystine ; 3 per cent, 

 of the total volume of gas must be deducted for glycine. 



Micro Apparatus i. 



Van Slyke [1913, i] described a smaller form of apparatus for use 

 in the analysis of amino acids in blood, tissues, etc., in which only 

 minute quantities are present. It may be advantageously used in 

 these estimations instead of the larger form of apparatus. Its dimen- 

 sions are : 



(i) The gas burette : 10 c.c., the upper part of 2 mm. diameter 

 measuring 2 c.c. and graduated in ^ c.c., the lower part wider and 

 graduated in -^ c.c. 



A gas burette holding a total volume of 20 or 30 c.c. is better as 

 frequently more than 10 c.c. of nitric oxide are evolved. 



This burette or its upper part should be enclosed in a water jacket, 



1 In later forms of apparatus another tube is sealed to D for introducing the capryl 

 alcohol. 



