140	QUANTITATIVE AGRICULTURAL ANALYX/ti
The series of buffer solutions suggested by Clark and Lubs
consists of mixtures of hydrochloric acid with potassium chloride
and with potassium acid phthalate, and of sodium hydroxide
with potassium acid phthalate, with moriopotassiurn orthophos-
phate and with orthoboric acid. By mixing these in stated
proportions and at stated dilutions the P// range is covered from
values of 1.2 to 10.0, in steps of 0.2.
Gillespie has described1 a method for dispensing with the use
of buffer solutions.
Applications.—A high degree of importance is attached to the
application of P// values to problems of agricultural and biological
chemistry. Mention may be made of the bearing of soil acidity
upon productiveness and upon adaptation to different crops; of
acidity of plant juices upon plant health and disease; and of
acidity of milk upon butter and cheese production. Hydrogen
ion concentration is of importance also in the culture and study
of bacteria, yeasts and molds; in the study of physiological
chemistry, particularly with relation to the digestive system and
the blood. Many other applications might be noted, of not so
direct interest to the agricultural or biological chemist and many
interesting lines of research have been opened up by the high
degree of development of this line of testing.
i Soil Science, 9, 115 (1920); /. Am. Chem. AW., 42, 742 (1920).