CHAP. I.] ' DIASTASIMETRY.' 57 



the liquid, acting during five minutes at a temperature of 40 C., to 

 the so-called achromic poin|,. the latter being recognized by the non- 

 production of any colour reaction on the addition of iodine. 



Thus if we state that in the case of human saliva D = 10 17, 

 we imply that 1 cubic centimetre of human saliva converts in a 

 period of five minutes from 10 to 17 cubic centimetres of standard 

 starch emulsion to the achromic point, the temperature being 

 40 C. 



Preparation Five grammes of pure potato starch are well 

 of standard stirred up into a thin mud with 30 c.c. of water, and 

 starch muci- fa[ s {$ then poured in a slender stream into 470 c.c. of 

 briskly boiling water. The mixture is stirred and 

 allowed to boil for a few seconds. Standard starch mucilage should 

 be used when fresh. After being kept for a few days it loses its 

 opalescent appearance and slight mucilaginous consistency, and is 

 then found to contain sugar. 



Preparation The solution of iodine is made by diluting one part 



of solution of of Liq. lodi of the British Pharmacopoeia with 200 

 iodine. parts Q f water> 



of the actual 10 c - c - f the standard starch mucilage are diluted 

 process of dia- to 100 c.c., and heated in a beaker over a flame to from 

 stasimetry. 40 45 C. A known volume, say 1 c.c., of the dia- 

 static solution is then added to the mucilage, and the time noted. 

 Then at intervals of a minute a drop of the enzymosing J^quid is 

 placed on a white slab with a drop of the iodine solution, and the 

 time and result of last testing is noted. When the achromic point 

 is reached the time is noted, and the interval from the commence- 

 ment of the experiment is computed. If at the end of three minutes 

 the mixture still gives the blue reaction of unaltered starch a new 

 experiment is made, using two, three, or four times the volume of 

 diastatic solution. If, on the other hand, the achromic point is reached 

 in less than two minutes, a new experiment is made, using a smaller 

 quantity of the extract. 



Two or three experiments generally suffice to determine the 

 quantity of diastatic solution required to bring the achromic point 

 within a period ranging from two to ten minutes. A final control 

 experiment enables the operator to fix the achromic point some- 

 where between four and six minutes. The accuracy of the method 

 depends chiefly on the sharpness or precision with which the occur- 

 rence of the achromic point can be determined. If it occur earlier 

 than two minutes the transition is too rapid for exact observation and 

 record. On the other hand, if it occur later than fifteen or twenty 

 minutes the transition is too gradual for precise limitation. The 

 most satisfactory results are obtained when 'the achromic point falls 

 between four and six minutes. The following example will serve as 



