56 ' DIASTASIMETRY.' [BOOK II. 



less accurate colorimetric methods, i.e., the amount has been de- 

 duced by comparing the intensity of the red colouration produced 

 by adding ferric chloride to a known volume or weight of saliva, 

 with the colour produced under exactly similar conditions when the 

 same iron solution is added to solutions containing known quantities 

 of sulphocyanic acid. By employing the method suggested by Hoppe- 

 Seyler for the determination of Haemoglobin, see Vol. i. p. 182, close 

 approximations may be doubtless arrived at. With the help of one of 

 the recently perfected colorimeters, as that of Dubosque or of C. H. 

 Wolff, still better results would be obtained 1 . 



Spectro- Professor Vierordt, employing the method of spectro- 



photometricai photometry to the estimation of sulphocyanates, de- 

 method, termined the extinction-coefficient of sulphocyanide of 

 iron, and on the assumption of its constancy and therefore of 

 the possibility of applying spectro-photometry to the solution 

 of the problem, made determinations of the amount of sulpho- 

 cyanate present in the saliva. Unfortunately it has been shewn by 

 the brothers Kriiss that spectro-photometry 2 is not applicable to the 

 determination of sulphocyanate of iron, inasmuch as the nature of the 

 compound formed varies within wide limits, and with these variations 

 likewise varies the extinction-coefficient and, necessarily also, the 

 ' absorption-relation/ 



Determination of the Diastatic Value of Saliva. 'Diastasimetry' 



It has been said that the enzyme which confers upon the saliva 

 of man and of some other animals its diastatic powers has not been 

 separated, so that we merely reason concerning the existence of the 

 body from a knowledge of its powers. Whilst we cannot estimate the 

 weight of the unknown body, we may determine the enzymic power 

 of any liquid containing it, the latter doubtless being, cceteris paribus, 

 in direct relation to the richness or poverty of the liquid in the 

 body. 



Principles of The diastatic value of a liquid, represented by the 



Robert's me- symbol D, may be expressed by the volume in cubic 



thod of dia- centimetres of a standard solution of starch mucilage 



stasunetry. which can be transformed by one cubic centimetre of 



1 For a description of this colorimeter consult ' Kolorimetrie und quantitative 

 Spektralanalyse in ihrer Anwendung in der Chemie,' von Dr Gerhard Kriiss und Dr 

 Hugo Kriiss, Hamburg und Leipzig, 1891. Wolff's colorimeter is sold by the optical 

 firm of Dr Hugo Kriiss of Hamburg for 100 and 130 marks. 



3 Consult 'Ueber das Absorptionsspektrum des Eisenrhodanides und die zwischen 

 Ferrisalzen und loslichen Khodaniden stattfindende Keaktion,' at page 174 of the pre- 

 viously quoted work of the brothers Kriiss. 



A thorough treatment of Spectro-photometry will be found in the 2nd edition of 

 Vol. i. of this work: a shorter account on a separate sheet accompanies this volume 

 for the use of the reader. 



