268 _ BOTANICAL GAZETTE [APRIL 
research in a concentration of 1.5 grams of iodine and 3 grams of 
potassium iodide per liter of water. 
In experimentation the various mixtures were placed in large 
test tubes (30 mm. in diameter and 150mm. deep), which were 
suspended through the suitably perforated top of a cylindrical 
water-bath. The water of the bath stood always at a higher 
level than that of the liquid in the tubes, which were some distance 
apart, the outer ones being several centimeters from the walls of 
the bath. It was thus assured that the mixtures in the tubes were 
maintained at the same temperature as the surrounding water. 
The temperature of the bath was kept nearly constant at 50° C., 
by means of an ordinary mercury regulator and a gas flame below. 
The variations in temperature were between the limits of 48° and 
52°. Since the computations of the velocity of diastatic activity 
were always made in terms of the velocity of the reaction in controls 
within the same series, the possible effects of temperature fluctua- 
tions should be exceedingly slight. 
A series of mixtures was usually prepared in the following 
manner: In each of a series of tubes was placed the proper amount 
of salt solution at a concentration in each case of four times’ the 
required concentration for each particular tube. To this were 
added 5 cc. of water, in the cases where the action of a single salt 
was to be tested, or an equal quantity of the solution of the other 
salt, in those where salt combinations were to be used; 8 cc. of 
starch paste (o.5 per cent) were then added to each tube, followed 
by 2 cc. of the previously prepared diastase solution. The tubes, 
containing 20 cc. of mixture, were immediately placed in the water- 
bath. It is thus apparent that all test mixtures contained the same 
quantity (0.2 per cent or 0.004 gm.) of the starch and of the 
diastase. 
An experiment was usually made up of (1) a series of 7 different 
concentrations of some salt used singly; (2) a series of 7 different 
concentrations of another salt used singly, and (3) a series, usually 
in duplicate, of the 7 concentrations of the two salts in binary 
combinations. These with the two control tubes made a total of 
7 For 2m mixtures ro cc. of the 4m stock salt stincasond wer Placed in Eee ~— 
this when diluted to 20 cc. by the addition of the st g 
concentration of the salt. 
