THE AMINO ACIDS 149 



recorded at the temperature and barometric pressure. The weight of nitro- 

 gen corresponding to the amount of nitrogen in the amino substance is cal- 

 culated or may be taken from the table compiled by Van Slyke and reproduced 

 on p. 607. 



In this table the allowance has been made for the evolution of only half 

 of the volume. The weights are therefore those for the amino nitrogen. 



During the measurement of the gas the bulb D can be emptied and washed. 

 A fresh solution of permanganate is not required for every analysis ; sufficient 

 is present in the Hempel pipette for 10-12 estimations. 



This pattern of apparatus has many advantages over the older pattern. 

 Some 6-8 estimations can be made in an hour. 



Micro Apparatus. 



Van Slyke l has also described a smaller form of apparatus for use when 

 only small quantities of material are available, such as in the analysis of the 

 amino acids in blood, tissues, etc. Its dimensions are : 



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

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

 in -^j c.c. ; a gas burette holding a total volume of 20 or 30 c.c. is more 

 advantageous as frequently more than 10 c.c. of nitric oxide is evolved; 



(2) the deaminising bulb: 11-12 c.c. ; 



(3) the burette : 2 c.c. 



The quantities of reagents required are 10 c.c. of sodium nitrite solution 

 and 2*5 c.c. of acetic acid for which the correction for impurities amounts to 

 o6--i2 c.c. 



It is not necessary to have a smaller Hempel pipette for permanganate, 

 With the micro apparatus the reagent in it lasts for a considerable time. 



The solution to be analysed may be introduced into the burette with a 

 pipette and the burette is washed with 6 or 7 drops of water. 



The error in the estimation need not exceed '005 mg. when 2 c.c. or 

 less gas is measured; with more gas '01 mg. 



With the micro apparatus one-fifth of the amount required for the 

 macro apparatus can be analysed. Not only is there an advantage 

 economically with reagents, but also the apparatus is less fragile. 



0-5 mg. of amino acid can be analysed with an accuracy of i per 

 cent. It is slightly more rapid: at 15-20 4 minutes' shaking suffice, at 

 20-25 3 minutes, above 25 2-2*5 minutes. 



It is essential that the burettes be accurate and the stopcocks be tight. 

 The burettes are tested by weighing the water they deliver ; the stopcocks by 

 submitting them to a pressure of a column of water i metre high. 



The apparatus may be cleaned with a mixture of potassium bichromate 

 and sulphuric acid. 



A still smaller form of apparatus may be used. 2 See 3rd edition "The 

 Chemical Constitution of the Proteins," Part I. 



*J. BioU Chem., 1913, 16, 121. z Ibid., 1915, 23, 408. 



