Feb.3,1923 Hydrogen-Ion Concentration and Varietal Resistance 375 
The hydrogen electrode was a piece of No. 24 platinum wire 18 mm. 
long, sealed in the end of a glass tube filled with mercury. The coating 
of platinum black was deposited in approximately 30 seconds from a 
3 per cent solution of platinum chlorid containing a trace of lead acetate. 
A freshly platinized electrode was used for each determination. 
The hydrogen electrode vessel was a stationary, closed cylinder of 
30-cc. maximum capacity, the liquid being thoroughly agitated by the 
hydrogen bubbling through it at the rate of two or three bubbles per 
second. Electrolytic hydrogen, freed from oxygen by being passed 
over a palladium asbestos heating coil, was used. It entered the elec¬ 
trode vessel through a side arm of the glass tube enclosing and supporting 
the hydrogen electrode, this tube being narrowed at the lower end for the 
length of 3 ie platinum wire constituting the electrode so that the bubbles 
of hydrogen washed down forcibly and broke over the end of the wire. 
Most of the measurements were made at a temperature of 25 0 C. 
in a small double-walled room, equipped with pipes with circulating 
water for cooling, a fan, and a heating coil automatically controlled 
by a Harvey thermoregulator. Temperature changes were noted and 
taken into account in making the computations. 
For calculating the P H values from file potential differences measured 
Michaelis’ (20, p. 15J-158) values for the saturated calomel cell and for 
the temperature coefficient were used. The presentation and com¬ 
parison of data are facilitated by using the simple P H units of Sorensen 
(25) rather than the numbers indicating the normality of the solutions 
in terms of grams of hydrogen per liter. Throughout this work the 
procedure was to make at least three successive determinations of each 
sample, and the average of these determinations was taken to represent 
the reaction of the juice. Measurements on the same sample practically 
always agreed within 0.02 P H . 
RESULTS 
hydrogen-ion concentration and varietal resistance 
Table I is a condensed summary of the results of the hydrogen-ion 
concentration determinations of the expressed juice of resistant and of 
susceptible varieties at various stages of development, and on which 
the varying environmental conditions acted in equal degree. Each P H 
value given is an average of the reactions of at least four varieties. 
Table I.— Hydrogen-ion concentration , in Ph units, of the expressed juice of wheat 
varieties in different stages of development and grown in different environments 
Environment. 
Age. 
Averages of 
resistant 
varieties. 0 
Averages of 
susceptible 
varieties. 
Approxi¬ 
mate soil 
reaction. & 
Germinating chambers. 
Weeks. 
I 
Ph 
3 - 96 (14] 
S - 8 9 ( 7 ) 
) 
Ph 
5 - 98 (is) 
3-92 ( 7 ) 
3 - 84 (14) 
Ph 
Greenhouse bench. 
I 
7.0 
Do. 
2-4 
5.86 (14; 
7. O 
Greenhouse pots (unlimed). 
4—6 
5 - 89 (ii] 
5 - 87 (5) 
7. O 
Greenhouse pots (limed). 
4-5 
6 -13 ( 7 ) 
6.14 (4) 
7. 5 
Field. 
6-7 
3-54 (7; 
1 
3-34 ( 4 ) 
7.0 
a The figures in parentheses indicate the number of samples averaged. 
b Determined colorimetrically with Wherry’s (34) set of indicators and a set of buffered color standards, 
for the use of which the writer is indebted to Miss Agnes Quirk, of the Laboratory of Plant Pathology 
Bureau of Plant Industry. 
